Apply clang format as proposed in T53211.
For details on usage and instructions for migrating branches
without conflicts, see:
https://wiki.blender.org/wiki/Tools/ClangFormat
The popover for displaying gizmos now has options for
empty, light & camera gizmos.
Transform toggles are now checkboxes, which has the advantage that it's
more obvious they can be mixed however changing from one to another now
uses 3x clicks instead of a single click-drag action.
We might need a faster way to switch between transform types.