Clean up some card issues

Summary:
Ref T2826.

• Adds a min height (arbitrarily, height of the gradient; other choices are 60px [title + avatar], or 70px [title + projects + closed + avatar]).
• Color bars 4px -> 6px.
• Fixes profile image clipping in Firefox, etc.
• Removes background color from avatars, for transparent GIFs and such.
• Fixes shift-click to select tasks in views that can't be grabbed.

Test Plan: {F37535}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T2826

Differential Revision: https://secure.phabricator.com/D5436