Moodle 3.1 and local_mobile deprecation

This issue only needs to be tested in 1 device. Install an older version of the app and login in a 3.1-3.4 site. Install a version of the app that includes this patch. Open the app. Check that you're sent to the reconnect screen. Enter the password and click to login. Check that you see a message saying that the app only supports 3.5 onwards. Go to add a new site, put the URL of a 3.1-3.4 site. Enter the credentials and click to login. Check that you see a message saying that the app only supports 3.5 onwards. Check that you can successfully login in a 3.5 site.