Add support for Awala apps on iOS

[gnarea]

Unfortunately, given the technical limitations that would prevent apps from communicating amongst themselves locally on the same iOS device, we can't have a standalone Awala app like we do everywhere else. So, we won't be able to offer the ability to sync with couriers on iOS -- meaning that iOS users won't be able to bypass Internet blackouts.

What we can do is to offer an iOS SDK so that apps can use Awala over the Internet, thus enabling their users to communicate with Awala-specific apps like Letro. They'll still benefit from the other advantages of using Awala, like spam prevention, for example.

See also #5.