Merge branch 'motd' into 'master'

Motd

Message of the day feature:  
An in the properties defined adminaccount can create a MotD that can has the audiences "students","tutors" or "all". e.g.: If you define a motd's audience as all, it will be shown on the FrontPage of ARSnova. A Message has start- & enddate to define the timerange, a title and a text which can be formatted via markdown.

See merge request !2

src/main/resources/views/motd

+{
+	"_id":"_design/motd",
+	"language":"javascript",
+	"views":{
+    		"all":{
+			"map":"function(doc) { if (doc.type == 'motd') { emit(1, doc);}}"
+		},
+		"admin":{
+			"map":"function(doc) { if (doc.type == 'motd' && doc.audience != 'session') { emit(1, doc);}}"
+		},
+		"for_students":{
+			"map":"function(doc) { if (doc.type == 'motd' && (doc.audience == 'students' || doc.audience == 'loggedIn')) { emit(1, doc);}}"
+		},
+		"for_tutors":{
+			"map":"function(doc) { if (doc.type == 'motd' && (doc.audience == 'tutors' || doc.audience == 'loggedIn')) { emit(1, doc);}}"
+		},
+		"for_all":{
+			"map":"function(doc) { if (doc.type == 'motd' && doc.audience == 'all') { emit(1, doc);}}"
+		},
+		"for_loggedin":{
+			"map":"function(doc) { if (doc.type == 'motd' && doc.audience == 'loggedIn') { emit(1, doc);}}"
+		},
+		"by_sessionkey":{
+			"map":"function(doc) { if (doc.type == 'motd' && doc.audience == 'session') { emit(doc.sessionkey, doc);}}"
+		},
+		"by_keyword":{
+			"map":"function(doc) { if (doc.type == 'motd') { emit(doc.motdkey, doc); }}"
+		},
+		"list_by_username":{
+			"map":"function(doc) { if (doc.type == 'motdlist') { emit(doc.username, doc); }}"
+		}
+	}
+}