move rightpanel into group view

res/css/structures/_GroupView.scss

@@ -15,10 +15,6 @@ limitations under the License.
 */
 
 .mx_GroupView {
-    max-width: 960px;
-    width: 100%;
-    margin-left: auto;
-    margin-right: auto;
     display: flex;
     flex-direction: column;
     overflow: hidden;
@@ -29,7 +25,6 @@ limitations under the License.
 }
 
 .mx_GroupView_header {
-    max-width: 960px;
     min-height: 70px;
     align-items: center;
     display: flex;
@@ -162,6 +157,11 @@ limitations under the License.
     line-height: 2em;
 }
 
+.mx_GroupView > .mx_MainSplit {
+    flex: 1;
+    display: flex;
+}
+
 .mx_GroupView_body  {
     flex-grow: 1;
 }