Make custom blocks for comments.
Store all comments in task object.
Add additional filters all comments to task objects.
Add additional templates for recent comments.

* Make current_time_utc required, and generate it at the start.
* Clean up logic in filters (including always showing the last comment
  at a minimum)
* Add 'as_date' filter for converting timestamps to date strings
* Add templates for last five comments, and last week's comments.
Fix bug with specifying sections without a colon.
Merge branch 'grab_all_comments'

Fixes #17.