Added project description, too
Restricting number of weeks to 4 (end-of-year corner case)
If you're editing an archived project, you get a nice fat warning title
Prevent editing of invoices on archived projects
Modified permission checks to account for archived projects/persons
Showing archived state when applicable
Archived persons are no longer editable on team page
Adjusted headings
Got booking filtering to work.

- Archived projects aren't bookable.

- Not-yet-active or not-active-anymore projects aren't bookable.

- You can only book in the current year
Allowing bookings in the next year, only not in the previous ones.
Added comment
Added totals to booking page
Added classes and IDs for later javascript counting of hours
Showing number of vacation hours left.
Updated changelog
Merge pull request #16 from nens/reinout-filtering

Reinout filtering