Added a way to show/hide frames and switch on/off colours. Also some minor work on the renderer itself and various minor cleaning ups.
Some minor cleaning up.

Just realised that my previous way of including headers might not be
compatible with older versions of Qt.
Some minor cleaning up.
Fixed some remaining issues with making the renderer use a floating point based approach.
Slight improvement to domToQwtMmlNodeType() and only paint known MML nodes.
Fixed an issue with rendering node frames and text.
Always paint the background of our formula viewer white.

So that we can easily check that colouring works fine.
Always show frames and colours.

Makes it easier to spot problems.
Allow the rotation to go up to 360 degrees.
Output the formula that is loaded.
Use the same 'normal font name' on all platforms.
Added support for drag & drop of an MML file.
Added some basic MML files and a file some useful links.