Make bulk_adder_spec idiomatic RSpec

* apropos of cleaning up the #success_message spec
Make BulkAdder append to tags, not overwrite
Render tags as list in .mapping-tags
Add individual tag styles

* Use tags in spans, links and lists
* Turn tags purple when they’ve been visited
Position tags in top right of mapping row

Known caveats:

* Existing line-break problems lead to more white space than is
necessary, the only way to deal with this is some form of smart
truncation
* When there is a very long original path and new URL the tags wrap to
a position between the path and new URL, which isn’t ideal
* Update tag list spec (wrapping class changed name)
Include help text when adding tags
Use consistent label margins in add mapping form

* This now matches the tag label/help text
Separate suggest URL and tag fields
Temporary workaround for other tests not restoring page size

* Needs fixing properly in another commit.
Add dismissible tags

* Split tags guide into parts
* Include dismissible tags
* Include tags being used as different font-sizes
  * Make spacing of tag relative to tag font-size