Add API call to get a channel by its name (#4700)

* add api for getByChannelName

* add tests

* fix test

* rename and tests

* check for permissions and test

webapp/client/client.jsx

@@ -1441,6 +1441,15 @@ export default class Client {
         end(this.handleResponse.bind(this, 'getMyChannelMembers', success, error));
     }
 
+    getChannelByName(channelName, success, error) {
+        request.
+        get(`${this.getChannelsRoute()}/name/${channelName}`).
+        set(this.defaultHeaders).
+        type('application/json').
+        accept('application/json').
+        end(this.handleResponse.bind(this, 'getChannelByName', success, error));
+    }
+
     getChannelStats(channelId, success, error) {
         request.
             get(`${this.getChannelNeededRoute(channelId)}/stats`).