UI changes

Known bugs:
- Date of first item is not displayed properly;
- Need to get rid of text-shadow on x-repost-dropdowns.

Motivation for changes:
- odd/even backgrounds on posts looked like dropshadows - flat colours look cleaner;
- white text-shadows on links make them stand out slightly better;
- unlabelling mentions make for easier reading and looks cleaner - normally these are used to display mentions in writing areas (publishers);
- right-border on hover is less intrusive than background-color changing;
- date-tab can be fiddly and get in your way by overlapping other posts - first post was inconsistent;
- font looks slightly better.

Changes that should go with this commit:
- Shorter TimeAgo (7s, 30m, 3h, 4d, 19 jan);
- Time should always be visible;
- Removing the "from SourceApp" from the date pane;
- Putting a picture of a more vertically aligned ^ or a @ in front of names. Personally I am really a sucker for the @ as people are so familiar with it.

Additional changes (requiring more work):
- Show SourceApp below the post upon clicking the post;
- Show "view conversation" link there as well;
- Eventually have a map there for posts with locations.

Last but not least, I rest my case: Green is more awesome! But I have been so kind to leave all the blue in. ;-)