Reduce the minimum user profile picture dimensions to 80x80 (to match our thumbnail size)

Currently, the field_user_picture field has a minium size requirement of 300x200 - which is actually rather big! Everytime I upload my "standard" user picture (which I use for all sites), it complains and then I have to find the uncropped version somewhere. Anyway, it's annoying. :-)

But also, this change is something that the Open Atrium team has been requesting for some time! They are already overriding this field to 80x80 and having success with that.

To help them out with their Valentine's Day release, I'm going to finally make this change.