Converter: use a DefineTemplate for compiler mode "delphi" when converting single unit files.

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41734 4005530d-fff6-0310-9dd1-cebe43e6787f
Converter: show settings dialog only once when converting many unit files. Improve settings GUI.

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41735 4005530d-fff6-0310-9dd1-cebe43e6787f
Converter: fix unit conversion in different situations. Issue #24527

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41736 4005530d-fff6-0310-9dd1-cebe43e6787f