notifications: rename are_now_dominus -> new_dominus

This notification will be used to let everyone know there is a new
dominus, there is no need to duplicate the notification. Rename to avoid
potential confusion.
notifications: create_notification_for_all_players

Helper method to easily allow sending a notification to all players.
Simply loops through all users and calls create_notification_new with
the appropriate parameters.
notifications: Send new_dominus notification to all users
notifications_global: filter out multiple new_dominus notifications

Uses the fact that each user has their own copy of the notification.
This should almost certainly be reworked to do one of
a. Remove the notification from the global panel
b. Create a new 'new_dominus_global' notification in place of reusing
   the existing personal notifications
c. Do the filtering on the server side
notification_new_dominus: Include lastDominusId in notification
notification_new_dominus: Wait for data to be ready before rendering

This is probably better handled in the parent template, when we provide
the data context. Here will do for now!
notification_new_dominus: Improve notification messaging

Uses the old Dominus to work out what a user's relationship to the
notification is when rendering. Could be extended to include the
what the game clock was set to at the time the notification was made.
notification_panel: Include current Dominus with game countdown
notification_panel: include last Dominus with game countdown

Only includes last Dominus if there is currently no Dominus.
Merge pull request #90 from Cogito/dominus-notification-tweaks

Dominus notification tweaks