Feature: Group liveries, and livery window usability enhancements. (#7108)

* Change: Replace checkbox in livery selection window with Default option in drop down selection.

This reduces clutter in the UI and allows for primary/secondary colours to independently follow the default scheme if desired.

* Feature: Add vehicle group liveries.

(svn r27730) -Change: Split openttd.grf into openttd.grf and orig_extra.grf
openttd.grf is now always loaded and provides all extra graphics in case the (possibly outdated) baseset does not.
orig_extra.grf contains graphics specific to the original baseset only.

(svn r23582) -Fix [FS#4870]: add missing characters for certain languages and the large font
-Codechange: don't remove large font glyphs because they are broken in the original font, just fix them up in openttd.grf using action A
-Change: make extra characters more consistent with the original font
All by PaulC.