Fix selected side panel title alignment
Fix selected side panel title alignment

This makes (border-bottom + padding-bottom + margin-bottom) the same
across selected and unselected tabs, avoiding a vertical center change
of 1/2 px.

Closes #107.

vlajos/firebug.next,vlajos/firebug.next,bmdeveloper/firebug.next,bmdeveloper/firebug.next,firebug/firebug.next,firebug/firebug.next