Compress PNGs used in new forms

I used `pngcrush -rem allb -brute -reduce`
The arrow* icons in this directory use 4-bit colormap and are even smaller.
pngcrush won't convert from 8-bit RGBA. Reedy or MaxSem might know how.

Change-Id: I5db98b1768aa14d392704f65ef647043ce96dd9a
Merge "Compress PNGs used in new forms"