Tweaks to annotation card styles

Picked off some low hanging fruit after a conversation with @dwhly on Thursday[1].

Dokku: http://card-tweaks.dokku.hypothes.is/

* Always right align timestamps on cards.
* Removed the dashed border on collapsed threads.
* Cleaned up the block quote styles.
* Swapped the expand/collapse icons to be consistent with other platforms.
* Remove the tooltip on the timestamp and with it a whole jQuery UI plugin. Now just uses the browsers native tooltip.

[1] https://docs.google.com/a/hypothes.is/document/d/1InGIlYIsibGM6zBCKexXAqvWRsGGCUuJ3bB8qG5ICvM/edit