Improve colour selection

Tapping the selected colour again will hide the panel
Improve drawing by ignoring touches immediately before a zoom gesture

Drawing operations started less than 300ms before a multi-touch
gesture are cancelled. This stops unintended drawing performed
when pinch zooming.
Merge branch 'feat/tool' into devel

Conflicts:
	app/src/main/java/com/jaween/pixelart/DrawingFragment.java
	app/src/main/java/com/jaween/pixelart/DrawingSurface.java