Add 'templateGroup' as a new 'container' option.

Coding.md: Beschreibung in Deutsch wie die Formularelemente , rekursiv, gerendert werden.
AbstractBuildForm.php: new function buildTemplateGroup()
BuildFormBootstrap.php, BuildFormPlain.php, BuildFormTable.php: Preparation for new optional TemplateGroup wrap.
QuickFormQuery.php: update comments.
formEditor.sql: column 'type' definition extended - new 'templateGroup' enum. FormElement 'type' updated to new container element 'templateGroup'