UI improvements

Summary:

• Don't show fragment on empty stop search result

• Use coordinator layout to avoid overlapping between Snackbar and buttons

Fix T899

Mitigation for T933

Test Plan: check it builds

Reviewers: valerio.bozzolan

Reviewed By: valerio.bozzolan

Subscribers: valerio.bozzolan, Libre BusTO

Tags: Libre BusTO

Maniphest Tasks: T899

Differential Revision: https://gitpull.it/D77