gui: DBDataModel: IdxDataManager: fixing problems with 'Universal node' created in non main thread
tr: ts file update
gui: ImagesTreeView: preparations for fix for issue #90

Gui is now refreshed more rarely.
Issue still needs some work, as gui blinks sometimes
gui: ImageTreeView: fixing never ending refresh
gui: ImagesTreeView: do not block refresh when window is being resized.

It was causing blinks while resizing
Merge branch 'issue_90' into development - fix for issue #90
IdxDataManager::appendIdxData: fixing situation when there are already children in item we append to
gui: ImagesView: using QPersistentModelIndex instead of QModelIndex in ModelIndexInfo (potential fix for issue #89)

It may happend to QModelIndex to be invalid when stored outside of Model
gui: ImagesTreeView: dead code removed
gui: ImagesTreeView: moving 'rowsInserted' to slots section
gui: ImagesTreeView: moving 'rowsAboutToBeRemoved' to slots section
gui: code cleanup
test: gui: fix for 'Data' test
gui: DBDataModel: IdxDataManager: adding assertions

make sure QModelIndex is valid
tests: gui: adopting to changes in gui; some fixes for existing tests
gui: ImagesTreeView: behaviour simplification in Data
tr: ts file update
gui: comments
tr: updating ts file
Merge branch 'issue_89' into development - fix for issue #89