Fix bugs; add GPL headers; improve structure

* Add GPL headers to files
* Move 3rdparty libraries files to src/3rdparty subdir
* Fix BCodeEdit scrolling on selectText and moveCursor calls
* Fix Enter key event handling in BCodeEdit
* Mark BCodeEdit as modified when splitting lines
Update translations
BeQt v3.1.6

* Add GPL headers to files
* Move 3rdparty libraries files to src/3rdparty subdir
* Fix BCodeEdit scrolling on selectText and moveCursor calls
* Fix Enter key event handling in BCodeEdit
* Mark BCodeEdit as modified when splitting lines