Always right align timestamps in cards

Move dropdown to the left of the timestamp to ensure timestamps are
always in line. Vertically align the baseline of the timestamp with the
username.
Remove dashed border on collapsed threads

It left a single pixel, which looked like a rendering glitch.
Clean up blockquote styles

* Remove cartoon quotes.
* Use a class rather than styling all blockquotes.
Correct expand/collapse icons on thread

Now collapsed items have a plus sign and expanded ones a minus. This
brings it inline with other tree view implementations such as those
found in Windows and Reddit where the icon represents the action
rather than the current state.