Offer "alias" field in room create form

Tries its best to not allow aliases that are too
long (full alias including leading #, : in the
middle, and homeserver domain name must not exceed
255 bytes.

Change-Id: I1e784a94cb599eca7e30736d666b20e37aad5444

src/i18n/de.js

@@ -21,6 +21,12 @@ export default {
       make_public: "Öffentlicher Raum",
       room_name_required:
         "Muss angegeben werden",
+      alias_required_if_public:
+        "Muss für öffentliche Räume angegeben werden.",
+      alias:
+        "Alias",
+      alias_too_long:
+        "Darf zusammen mit der Domain des Homeservers 255 bytes nicht überschreiten"
     }
   },
   resources: {

src/i18n/en.js

@@ -21,6 +21,12 @@ export default {
       make_public: "Make room public",
       room_name_required:
         "Must be provided",
+      alias_required_if_public:
+        "Must be provided for a public room",
+      alias:
+        "Alias",
+      alias_too_long:
+        "Must not exceed 255 bytes including the domain of the homeserver."
     }
   },
   resources: {