Improve avatar appearance

Avatars are now 38x38pt (75x75px) with 4pt-radius rounded corners.

Adjust avatar box based on whether the device screen is Retina.
Add detail view to collection cells

For now simply display the attributed text with no avatars or user handles.

The toolbar is currently not visible.
switch to OHAttributedLabel
Improve content detail view layout

Also extend relative date functionality with an additional method.
Allow user to set font of BasicHTMLLabel instances

This has to be accomplished by adding font attribute to
the attributed string instead of using the default setFont
method.
UI changes

Use serif font for comment body, allow SDK user to set line spacing without subclassing,
revert to using smaller avatars (25x25pt for now), display higher-quality avatars in
detail view for content.
Merge pull request #5 from Livefyre/dev

Dev