This adds the following UI:

archive and mute buttons in a Hide dropdown menu in a review request view
banner that indicates that review request is archived with an unarchive button
banner that indicates that review request is muted with an unmute button

Review request visibility is now passed as context data to templates. If visibility is VISIBLE, the Hide dropdown menu becomes visibile. If visibility is ARCHIVED or MUTED, the Hide dropdown menu is hidden and the appropriate archive or mute banner appears. When visibility is changed, a page refresh is triggered.
This also augments the UserSession WatchedItem (renamed StoredItem) to also include archivedReviewRequests and mutedReviewRequests. The only difference these objects are their URL and their error messages (addError and removeError methods were added in order to set different errors).

Archived and mute banner tests were added to reviewRequestEditorViewTests.js, all tests passed.