PLT-6481 Create platform route and logic to be able to DM a user by email or username (#6310)

* Add logic to be able to DM a user by email or username

* PLT-6481 update DM url to be in the format https://servername.com/teamname/messages/xxxxxxxx

* PLT-6481 Adding logic to get user by full email

* PLT-6481 logic for routes /messages/user_id and /messages/id1_id2 to redirect to /messages/@username

* PLT-6481 logic for GM route /messages/generated_id

webapp/stores/user_store.jsx

@@ -232,6 +232,10 @@ class UserStoreClass extends EventEmitter {
         return Selectors.getUsersByUsername(store.getState());
     }
 
+    getProfileByEmail(email) {
+        return Selectors.getUsersByEmail(store.getState())[email];
+    }
+
     getActiveOnlyProfiles(skipCurrent) {
         const active = {};
         const profiles = this.getProfiles();