Merge pull request #308 from topilski/master

BSON Undefined type doesn't rendered to string correctly #306
QToolBar style removed
QToolBar separators removed, because they were drawn automatically on Windows
_id field existence check and minor UI tweaks
WorkAreaWidget added in order to set correct padding of inner tab widget
Padding between indicators corrected
0.8.3 beta 2
Menu items text changes, larger Document Editor with added maximize button.
Delete WorkAreaTabWidget