Move action.watch to a more suitable place and expose updateWatchLink

Move action.watch to a more suitable place and expose updateWatchLink
method in mw.page.watch.  Update method to toggle watch, unwatch
list item id attribute.
Patchset 2- Expose method with less code duplication, restore
comments, cleanup whitespace.
Patchset 3-5 Whitespace cleanup
Patchset 6 - Trigger a watch event on the updated li
Patchset 7 - Only trigger watch event if not updating
state, announce opposite of icon action, to properly
indicate action taken.
Patchset 8 - Cleanup spacing and comments issues,
change event namespace.
Patchset 9 - actually add the change
Change-Id: I591f9f847db391c5d1477dc2ed41de54ec266261