Use new MotD views

The following replacements have been made:
* New design document name
    - New view name: (conditions) keys => values
        * Full old view name: (conditions) keys => values

* motd/
    - by_motdkey: motdkey => _rev
        * motd/by_keyword: motdkey => doc
    - doc_by_audience_for_global: (audience != 'session') audience => doc
        * motd/admin: (audience != 'session') 1 => doc
        * motd/for_tutors: (audience == 'tutors' || audience == 'loggedIn') 1 => doc
            - 2 backend requests
        * motd/for_all: (audience == 'all') 1 => doc
        * motd/for_loggedin: (audience == 'loggedIn') 1 => doc
        * motd/for_students: (audience == 'students' || audience == 'loggedIn') 1 => doc
            - 2 backend requests
    - doc_by_sessionkey: (audience == 'session') sessionkey => doc
        * motd/by_sessionkey: (audience == 'session') sessionkey => doc
* motdlist/
    - doc_by_username: username => doc
        * motd/list_by_username: username => doc

The following views have been removed:
* motd/all: 1 => doc (never used)