Convert view_user dispatch to prove the conversion works

This is a relatively obvious dispatch action that doesn't require a lot of complicated type definitions, so should be a good candidate to prove the thing works. If for some reason the thing stops working, we've done something wrong.

This also adds a bit of generic types to the dispatch call so we don't confuse the tsx parser by using `dis.dispatch(<ViewUserPayload>{...})` as it thinks that's supposed to be a component. We still get type safety, and the thing remains happy with the generics approach.

src/components/views/groups/GroupMemberInfo.js

@@ -28,6 +28,7 @@ import GroupStore from '../../../stores/GroupStore';
 import AccessibleButton from '../elements/AccessibleButton';
 import MatrixClientContext from "../../../contexts/MatrixClientContext";
 import AutoHideScrollbar from "../../structures/AutoHideScrollbar";
+import {Action} from "../../../dispatcher/actions";
 
 export default createReactClass({
     displayName: 'GroupMemberInfo',
@@ -103,7 +104,7 @@ export default createReactClass({
                 ).then(() => {
                     // return to the user list
                     dis.dispatch({
-                        action: "view_user",
+                        action: Action.ViewUser,
                         member: null,
                     });
                 }).catch((e) => {
@@ -124,7 +125,7 @@ export default createReactClass({
     _onCancel: function(e) {
         // Go back to the user list
         dis.dispatch({
-            action: "view_user",
+            action: Action.ViewUser,
             member: null,
         });
     },