Issues/1098 better admin selects

:warning: Work in progress :warning: 

Closes #1098 

I'm not sure I'm happy with all of this pull request. It has highlighted that there are bits of the admin not working (the `ajax_select` 404s - #1101) and that the jQuery we rely on is now provided as a side effect of using the `django-markitup>=2.1 (added in c5fdf97df10782c098592e89503fce461840dcda) - which I think is likely to be brittle.

There are also no tests, but there should be. There are existing selenium tests for the ajax_select (if memory serves) and hopefully these will be failing when the tests are run (some setup twiddling required to do that).

Also currently only a few of the many possible admin parts that could use the autocomplete are using them, #1102 is for adding it more widely.


Before:

![change_info_page___pombola_site_admin-2](https://f.cloud.github.com/assets/187630/1743746/a09fe340-6411-11e3-9ef4-c41a72d3810d.png)

After:

![change_info_page___pombola_site_admin](https://f.cloud.github.com/assets/187630/1743737/8a9aa81e-6411-11e3-9ec4-f388311296d4.png)