Manual.rst: Best practice default values.

DRAGANDDROP.md, PROTOCOL.md: Doc for "drag'n' drop" implementation.
dragAndDrop.php: API endpoint
DragAndDrop.php: Class for implementing drag'n' drop functionality.
Link.php: implement new renderMode=8 - returning only the sip.
QuickFormQuery.php: New entry point for processing "drag'n' drop".

Feature 5425 / thumbnail: rewrite - secure thumbnails are now rendered on first access, not when 'AS _thumbnail' is called.

Feature 5425 / thumbnail: rewrite - secure thumbnails are now rendered on first access, not when 'AS _thumbnail' is called.

Implemented: New > Close (save) now closes correctly the current page. Addtional, #1930 has been solved implizit.

Sanitize.php, FillStoreForm.php,  Store.php, Manual.rst: Corrections. Replace 'sanatize' against 'sanitize'.

QfqForm.js: Preparation for client, to handle window.location.replace() by new API status 'url-skip-history'. Also changed "(data.redirect === "url" || data['redirect-url'])" to "(data.redirect === "url" && data['redirect-url'])" - CR did not understand the former logic ('or' instead of 'and'). #OPEN#: window.location.replace = 'index.php....' throws an JS exception that it the attribute 'replace' is readonly. Instead "window.location.replace('index.php....')" works as expected.
PROTOCOL.md: add 'url-skip-history'.
save.php: recode to become more readable.
QuickFormQuery.php: getForwardMode() - temporarily fix to update status 'page' to 'url' (bug never caused a problem as long as '||' has been used on client side). Will change 'page' to 'url' asap.

PROTOCOL.md: added 'the attribute' in one sentence