Filter form tweaks

- date time picker starts on month view (easier for skipping back a few
  years)
- let django-filter build the form for filtering by parameters
  automatically
- add a reset button (because django-datetime-widget doesn't let you
  clear the field once you've picked a date
Make static URLs neater with the `static` filter

Also fixed the github link to point at the new repo & use https URLs
for gh + twitter.
Merge pull request #31 from jimr/links

Make static URLs neater with the `static` filter
Merge pull request #30 from jimr/filter-form-tweak

Filter form tweaks