CSS tweaks for tags, search, and other small things

 * Gave tags square corners, made them smaller, and slightly opaque.
 * Made tags left justified with text above and below.
 * The topbar is back to its original height
 * Old: The "share" url box no longer obscures the controls along its lower edge.
 * The space between different facets in the search bar is now a touch tighter.
 * Put highlight and lock icon on same line as username.
Merge pull request #656 from hypothesis/CSStweaksV1-2

CSS tweaks for tags, search, and other small things