(bug 44253) Add message when there are few watchers

When a page has fewer than $wgUnwatchedPageThreshold watchers and the
user does not have the 'unwatchedpages' right, the row for number if
watchers is not being displayed at all. This is confusing to some users,
so instead display the row with an appropriate message.

Change-Id: I2425e45ec5db2dc743f875acf3fd3717b7d06286
Merge "(bug 44253) Add message when there are few watchers"