Add ability for NumberTextCtrl to accept decimal numbers
Make OGLCanvas refresh timer settable
Fixes/improvements to LinePropsPanel

- Save sector tag correctly
- Implement 'New Tag' button
- Add line id field (for UDMF)
- Use NumberTextCtrl for number text boxes
Add custom properties dialog for things
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git