Added drawing functionality.
Added UI drawing widgets.
Added brush color and radius functionality.
Added undo/redo functionality while drawing.
Performance optimizations while drawing.
Saving the drawn image now can be done in a separate thread without an OpenGL context.
Now drawn image is saved in a background thread.
Optimized drawing memory usage. Now only keeps the minimum pixmap rectangle necessary to perform undo/redo.
Fixed null pointer exception while releasing drawn resources.
Improved line accuracy while drawing.
Added a dot if the user clicks without dragging a line.
Fixed other line-related bugs.
Improved dot drawing quality.
Fixed a bug triggered while saving an empty image.
Improved drawing boundary behavior.
Drawing code refactoring.
PaintingWidget ~> BrushStrokes.
Added javadocs explaining how the drawing process is implemented.
Fixed resize bug while drawing.
Minor code cleaning.
Merge pull request #319 from RotaruDan/paintingWidget

Painting functionality.