Displaying creation and modification dates.

* Fixes the  `{{{#!python` to `{{{python`
* The author is displayed with both identities `trac (@github)` for the
  ones with fanciful Github login (like I do)
* creation date is displayed for tickets and comments
* update date is displayed for tickets if different than creation. As
  changes cannot be undone or edited, there are no update dates for
  the comments.

**NB:** I only tested it off-line by outputting to stdout