Allow package metadata viewed on the website to be editable

Fixes #807 'Allow package metadata to be editable'. This does not update nupkg files, that will probably end up as a separate PR against the worker role (have not started it yet).

Also partially fixes #35 'Store tags in a separate table'.

Edits to package metadata are reflected in API v2 feeds and search results (after a few minutes) as well as the package details page.

![StrawManUI](https://f.cloud.github.com/assets/2711795/431911/352b31da-ae97-11e2-92f6-19a25cf2dfff.png)