minor changes to ycm script
scale up images for Retina screens
Scale down avatar images for non-Retina screens

Turns out that scaling up avatars for Retina causes them to look
ugly so choose to scale down avatars instead when not using a
Retina screen.
Set imageFrame in one operation

Also fix some comments.
Right-align dates and time label text

Every piece of content now has a pretty right-aligned relative
time/date label.