Add support for coroutines

[dabitdev]

The current CashImpl implementation of Cash SDK uses listeners to return the values.
It should be interesting to support co-routines instead of listeners.
For example:

fun login(network: BtcNetwork, phoneNumber: String, listener: Cash.WacCallback) 

With co-routine

 suspend fun login(network: BtcNetwork, phoneNumber: String): Result<WacCallback>

[herou]

@dabitdev Please, check this PR #40

[herou]

@dabitdev You can assign to me other tickets.