Add a new "paste_button_callback"
phpdoc and removed the & from the DC variable in paste button callback as the DC is
always passed by reference and therefore does not have to be passed as variable.
do also call the paste_button_callback for the root element in the header.
- Do only call the paste_button_callback once instead of twice.
- Do not add the default buttons if the callback returned a proper value.
renamed oncreate_callback in constructor to tablename_callback to avoid collision
with record oncreate_callback which is present since Contao 2.9 and already broke
DC_DynamicTable.
So the dynamic table behaviour can now be gained via tablename_callback.
Merge branch 'dev'

Conflicts:
	system/modules/generalDriver/InterfaceGeneralCallback.php
bugfixing paste into & paste after in mode 5.