Add FIXMEs for the withRouter workaround

Because of: https://github.com/ReactTraining/react-router/issues/5795
We have to use withRouter which triggers a lot of extra renderings.
This means that until the bug is fixed we have to use withRouter and
some memoization to make sure we don't recalc everything all the time.

src/Root.tsx

@@ -66,6 +66,7 @@ const mapStateToProps = (state: StoreState) => {
   };
 };
 
+// FIXME: withRouter is only needed here because of https://github.com/ReactTraining/react-router/issues/5795
 export default withRouter(connect(
   mapStateToProps
 )(Root));

src/SyncGate.tsx

@@ -145,6 +145,7 @@ const mapStateToProps = (state: StoreState, props: PropsType) => {
   };
 };
 
+// FIXME: withRouter is only needed here because of https://github.com/ReactTraining/react-router/issues/5795
 export default withRouter(connect(
   mapStateToProps
 )(SyncGate));