Autolayout and Xcode 6 xib support

Added support for auto layout's intrinsic content size calculations, so
that this view can be sized automatically by auto layout without
explicit width/height constraints.

This also includes an attempt to expose some properties as editable via
Xcode 6's new attribute editing feature with IBInspectable properties
for a few things. I tried adding that to the image as well but it
didn't appear in Xcode properly, most likely due to the typedef for
images.