* Recode the '_link' notation for download
* Add 'ZIP' as export format
* Add 'parameter' to wkhtmltopdf
* Implemented 'SYSTEM_STORE / SYSTEM_DOWNLOAD_POPUP' for detecting if there are download links on the page. This eleminates passing parameters through dozens of functions.
* Report/Columntype '_dDownload' broken!
Coding.md: described `download` from a coding point of view.
Manual.rst: Update '_link' to latest notation of 'download'.
download.php: implemented catching of 'Undefined index'. Added further exceptions.
Download.php: Added cache=off for downloading. Rename getFile() to getElement(). Make getElement() more generic. Add zipFiles(). Implement 'downloadMode' in doElements().
Html2Pdf.php: recode to new download notation. Parameter to wkhtmltopdf implemented.
Link.php: New TOKEN_* and NAME_DOWNLOAD_*, NAME_FILE. Move TOKEN_* to Constants.php. Will be used in Download.php too. Implemented 'SYSTEM_STORE / SYSTEM_DOWNLOAD_POPUP'. Implemented BASE64 encoding of multiple 'U' and 'u'.
Report.php: Implemented 'SYSTEM_STORE / SYSTEM_DOWNLOAD_POPUP'.
Sip.php: implement debugSip() to show Sip. New: base64 encoded parameter will be shown in clear.
Store.php: some functions missed keyword 'static'. getVar() and getStore automatically decode base64 parameter.
QuickFormQuery.php: Implemented 'SYSTEM_STORE / SYSTEM_DOWNLOAD_POPUP'.

Implemented spinning wheel (hourglass) displayed during rendering and downloading PDF.
Link.php, Report.php: New $vars[NAME_EXTRA_CONTENT_WRAP] which holds a '<button>' definition with necesary 'data-*' attributes. The Modal Dialog needs a uniq html id (derived from ttContentUid). That one is returned to Report() if there is at least one download element.

Implemented spinning wheel (hourglass) displayed during rendering and downloading PDF.
Link.php, Report.php: New $vars[NAME_EXTRA_CONTENT_WRAP] which holds a '<button>' definition with necesary 'data-*' attributes. The Modal Dialog needs a uniq html id (derived from ttContentUid). That one is returned to Report() if there is at least one download element.

Implemented download.php to offer SIP protected downloads for single files (any filetype) as well as concatenated PDF files and converted HTML pages.
download.php: API Interface
DownloadException.php: New exception class for downloads - might be extended for better error handling.
OnArray.php: new function getArrayItemKeyNameStartWith() to filter for specific elements in an array. New function arrayEscapeshellarg() to escape args
Download.php: Main class.
Link.php, Report.php: implemented new link type 'd' (=download)

Split PHP 'print.php' in a pure API file 'print.php' and a class 'Html2Pdf.php' - the class will be reused by Download.php

Manual.rst: Prefetch doc enhanced.
Ldap.php: replacement of '?' in LDAP search not processed with MODE_LDAP_PREFETCH - fixed. FE_TYPEAHEAD_LDAP_KEY_PRINTF renamed to FE_TYPEAHEAD_LDAP_ID_PRINTF
AbstractBuildForm.php: copy 'FE_TYPEAHEAD_LDAP_ID_PRINTF' to SIP seems never be done - fixed

#3552 / typeAheadLdapSearchPerToken - webpass kann nicht gleichzeitig nach Vornamen und Nachnamen suchen
After discussing with EV it's not necessary  to permut the serach, instead just repeat the whole search with every token. Quite simple and effective.

#3552 / typeAheadLdapSearchPerToken - webpass kann nicht gleichzeitig nach Vornamen und Nachnamen suchen
Neuen Modus 'typeAheadLdapSearchPerToken' implementiert.
Manual.rst: neues Feature dokumentiert.
Ldap.php: Neue Funktion 'explodePermutSearch()'.

During expanding of templateGroups, existing FE with no meaning for save (like note, subrecord, ...) has been created, filled with empty values and saved. Fixed for FEs with type 'subrecord' and 'note' - needs more investigation to check for further sideeffects.

Action elements, assigned to a container which are not a templategroup, threw an exception. In general, it makes no sense (at the time of writing this) to assign an action element to a pill or fieldset, but it should not throw an exception. Fixed - just ignore such assignment.

Throw of a UserFormException with wrong parameter. Fixed.

The new class T3info() was fine, but relying classes assumed that all array elements always exist. This was not given in the past. The new implemention creates at least an empty entry for each element.
AbstractException.php: removed garbage line.
save.php: require_once missing PHP Exception classes.
T3Info.php: recode.

Implemented.

#3536 / a) Datum (datetime / timestamp) werden nicht angezeigt, b) Angezeigte Datumsformat String und aktzeptierte Eingabe matchen nicht
Neu wird bei QFQ date/time/datetime kein HTML INPUT type=date|time|datetime-local mehr generiert, sondern ein 'text' - damit verlieren wir die Browserinternen Datepicker (Chrome, Opera) aber gewinnen die Kontrolle die Datumsformateingabe zurueck.