Darker labels in new login and create acct forms

Bug: 47777
Change-Id: I01dd960d673a37d519ae8805db1fbbcb5a4306c9
(cherry picked from commit 331cca078947dcd9fd0c925b810685ec17f72ec4)
Compress PNGs used in new forms

I used `pngcrush -rem allb -brute -reduce`

Change-Id: I5db98b1768aa14d392704f65ef647043ce96dd9a
(cherry picked from commit 5decaffd6dea4f6643e3e23de2dc55c437a3f0b7)