Simplify icon handling

Eliminate the pointless runtime command name -> icon map and just make
commands responsible for their icons. Don't bother predecoding and
caching icons since it wastes some RAM (~10 MB) and decoding icons takes
a trivial amount of time.

Fix a few places where icons were being set for the wrong command names.
Simplify HelpButton a little

Switch to flat_map for trivially less memory usage and just use a global
map rather than a heap-allocated map since it's not
(de)initialization-order sensitive.
Add 48x48 and 64x64 icons
Use retina icons for the main toolbar if first opened on a retina display
Dynamically switch to the retina toolbar icons as appropriate
Retinafy the video display
Update Indonesian translation