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
Because in general, I've found it preferable not to style the base elements and always use classes. Otherwise as the application grows you end up having to add css to reset each block quote when you want to use the same element but a different style. We've seen this already with the base input styles, and the search bar.

By sticking with classes you're always working against the browser defaults.