Fixed SQL queries for inserting groups as watchers so they work with Postgres ; Added a link to the group list (if we have the Redmine People plug-in available)

--HG--
extra : amend_source : 538501593ff755bc6546e833e0d4164881449837
Adding japanese locale for watcher groups
Fixed japanese locale header for ja.yml
Added watcher tracking via journal entries (not final form, it just stores a plaintext message) by overriding the set_watcher() method and expanding upon set_watcher_group(), fixed a few more localized labels
Not actually needing lib/watcher_groups_controller_patch.rb
Added the current user name in the message, and modified the locales entries accordingly. (Fixes #21302)
Fixed a message problem in english (Related to #21302)
Cleaned up the code and add_watcher_journal() calls, moved Issues.set_watcher_with_journal() in InstanceMethods, patched WatchersController#create for journal addition, fixed labels a bit, given that now we use one message for addition of multiple watchers.