(Bug 4813) Create a new page /admin/importer/history

* accessible to supporthelps
* lists all the user's imports + current status for each item + time the
  import was scheduled + time the import was last processed
* moved /admin/importer to /admin/importer/queue (including updating the
  link), to prevent confusion since the /history isn't a subset of the
  queue
(Bug 4813) Tie to siteadmin:importhistory priv
Merge pull request #227 from afuna/support-tool-import-history-bug4813

(Bug 4813) Create a new page /admin/importer/history