Add colour picker and various fixes

The Customise button opens up a colour picker fragment.
It contains a HSL colour wheel with sliders.
This is still a work in progress and hasn't been tested
on different screen sizes.
Improve layout on various screen sizes and densities

Panels slide in from the top on portait phone screens and
from the side on landscape phone screens. On larger screens
the panels are either combined into a single side sliding
panel or remain static onscreen if enough room is available.