CSS Improvements

+Moved time closer to right hand side of annotation card (closer to triangle).
+Used same style as search x for notifications.
+Added onhover underline for usernames to make it more obvious they are links
+Fixed time position when "show differences" is checked.
+Revised standalone annotation page.
+Made slight improvements to streams CSS.
+Fixed bug where pull quote would not show for highlights. [Issue 709](https://github.com/hypothesis/h/issues/709)
+Fixed: top bar on streams should stick to top of page and not float
+Fixed collapsed annotation font light/dark difference.
+Revised stylings for notifications 

You can test out the changes at http://csstweaks.dokku.hypothes.is