As a watchlist expiry user, I want to be able to watch a page via edit, so that I can temporarily watch a page after a recent edit.
**Resources:**
* [[ https://meta.wikimedia.org/wiki/Community_Tech/Watchlist_Expiry | Watchlist Expiry project page ]]
* [[ https://wikimedia.invisionapp.com/public/share/J911SKRX3U#/screens/475686102 | Interactive mockup: Watch a page temporarily (via edit) ]]
**Acceptance Criteria:**
* When user checks the box to "Watch this page" in edit view, a drop-down should appear/become active next to the checkbox
* The user should be able to select watch period via drop-down
** The drop-down has the following options:
*** Permanently (as default)
*** for 1 week
*** for 1 month
*** for 3 months
*** for 6 months
* The watch period should be saved or updated based on selection
* If the page has already been watched, the behavior should be as follows:
** Drop-down should have days left as pre-selected option at top
** The selection should be written as follows: "X days left" (for example, "10 days left" or "20 days left").