Epic commit.

Improvement:
1. Added editNodeDialog that shows up when you dblclck on Node in graph
or listView. It has some possibilities to change data: name, path,
color, comment (in future), connectionList (in future).
2. Added saving and loading color of node and it's name (also for edge,
but you can't still change this parameters).
3. Renamed saveRoles in GraphModel to Ref roles so that it is more
logical.
4. GraphView is in charge of handling openEdit() functions.
5. A couple additional functions in GraphVisNode like setNameText() and
setColor().
6. Fixed memory leak in GraphNode::setFileInfo() function.
7. Functions in GraphScene: nodes(), selectedNodes(), cg() /*center of
gravity*/.
8. openFile() in MainWindow so that we can load recent files using
QSettings.
9. Goes from 8. - now the programm will load last used graph at start of
the programm.
10. Settings now store the dirs where you last time opened/saved files.