No-JS bulk tagging of existing mappings

* We subvert the purpose of params[:http_status], allowing 'tag'
* We use a BulkTagger class with the same interface as BulkEditor
BulkTagger existing mapping behaviour should:

* Remove common tags removed from tags field
* Add or ensure presence of other tags
* Leave non-common tags alone
Let steps know via @_javascript if they're JS
Bulk tagging via JS modal

* still abusing http_status as a 'tag' vehicle
Stop abusing http_status. Rename to "operation"
http_status_name comment moved to operation_name
Remove BulkTagger#common_data
DRY up supported HTTP statuses in bulk adder/editors