Add a message to the map view if no map tiles are available (either no
network, or no SD card).
issue 898, notification not bringing app to front, fixed, this was
unhooked during UI refactor
Merge pull request #905 from garvankeeley/warn-no-map-tiles-rebase

Add a message to the map view if no map tiles are available
Merge pull request #906 from garvankeeley/issue898-notification

issue 898, notification not bringing app to front