Warn user about refused location permission

[ialokim]

Only little issue I have, but idk if it's supposed to be normal, is that Transportr never asks me again about the location permission once I refuse (even if I click on the grey locate button).

Originally posted by @Altonss in #912 (comment)

comment by @Kelvino9:

In Organics Maps you'll be notified to change location permission manually once you denied location permission.

I agree that Transportr should somehow inform the user of the missing location permission, but only when explicitly requested by the user (by clicking the greyed-out locate button), and not (as Organic Maps seems to do it) on every start of the app.