Fix post list breaking when post's tags aren't yet loaded

* Restore Tags.fetch() so we probably have tags when posts are loaded.
* Wrap Post.getTags() result in _.compact() to remove falsy values that
happen when a tag isn't loaded yet.
Switch tag collection to clientside paging so we get all tags at once

This means we can use the full tags collection when get tag info
for posts, but still have paging for the tags admin. Ideally paging
should be seperate from the collection, but this is what we have for now.
Give testing users password ("testing") so I can login after running tests
Merge pull request #215 from ushahidi/fix-post-list-tags-error

Fix post list breaking when post's tags aren't yet loaded