Pre-defined list of tags to use (only)

- Load in the list of tags from the DB, to use as an allowed list of tags, and also as
an auto complete list
- disable local storage, as this could cause inconsistencies with list for tagmanager
  and the list for typeahead
store tags URL in one place and reuse
remove auto save as it was causing new tags to be saved

- auto save wasn't working for the CKEditor anyway, so had
  limited value
- ensure that tags sent through on save are ones in the
  valid list
- ensure that random chars entered into keywords input
  weren't saved as new tags on publish
added strict equality
Merge pull request #55 from moneyadviceservice/restrict_tags

Restrict tags