Add an option to fake user's location

Take a look at how it's done here: https://github.com/mcastillof/FakeTraveler

We can do pretty much the same on Android.

Here's how it can be done:

1. Provide an advanced setting that "mocks" user's location.
2. We should add a whole screen for this feature and put the detailed explanation on how to enable it.
3. We should either let the user choose the specific location OR just re-use the endpoint's location.

@denis9229 what do you think about it?