Change to implement a field in a topic indicating the related task from the
project to which the forum is related.
On the 'View Task' page there's now a new tab 'Forum Topics', to show the
posts related to the task from whatever forums.
On the normal message view the related task is shown at right.
Fix to make sure that the associated field's onchange event triggers when
the date is changed in the calendar (needed to submit on changes to the
text field).
Make the login and logout history descriptions more, well, descriptive.
Changes to the history module:

- The History can now be filtered by period.
- The permission test is now done before counting history items, avoiding
  get an item and page count that does not match what is shown.
- Some label descriptions changes.