Display last translator gravatar next to the editing area.

Also adapted other gravatar's markup for consistency and removed unneeded extra
markup.

Fixes bug 2405.
Simplified code by using setdefault.
Removed dead code.
Use insertAfter for proper resulting markup.
Display the date of the latest edit below the edit box.

Now if the latest entry in the timeline refers to a change made only to the
target, it's not displayed again as part of the timeline, since the information
is already available as part of the current unit status.

Fixes bug 2702.
Some layout fixes.
Moved the code to generate relative dates to the client-side.

Since template fragment caching is used for edit units, it would always report
the same relative datetime. By moving these calculations to the client, we
always get an accurate relative datetime which is periodically updated.

Fixes bug 2706.
Several layout fixes.
Make last translator's gravatar more prominent.
Avoid animation glitches when toggling visibility.
Display comment's date and time.

This aligns with other parts of the timeline. Also refactored comment templates
to avoid repeating the same markup.
Provide proper separation for suggestions.
Fixed template indentation.
Unified markup.
Removed unused code.
Don't display timeline link if there's nothing to be shown.
Small cleanup.
Improved code readability.
Use the same time for all submissions.
Attribute proper submission information upon suggestion approval.