ColorPickerViewController replaced by ColorPicker, a subclass of UIControl.
Stroke color changing.
Revert "Stroke color changing."

This reverts commit b324e78b82e6c33f15f7e8b182f0144a220d9622.
Stroke color changing.
Color button changing color accordingly.
Tools added.
Color wheel image cleaned.
Tool presets.
Clear screen button added.
Strokes moved to Painting model class.
Small CanvasController refactorings.
Prerendering implemented.
Splitting long lines. Clear screen logic.
Sensible default prerendering settings.
Few bugs fixed.
Highlight active tool button.