1. Add options to the Practice and Practice Location to set the:
- background colour (used for the left and top menu)
- accent colour (used for buttons and dialog titles)
If a Practice Location doesn't set any colours, they are picked up from the Practice.
2. Change the button rollover colour to be a lighter shade of the accent colour, or a darker colour, if there isn't enough contrast
3. Derive font colours based on accent colour. i.e. if the accent colour is closer to white, choose black; if the accent colour is closer to back, choose white
4. Remove the theme.colour, theme.title.colour, theme.button.colour, and theme.selection.colour from default.properties