Improve wording on iOS when no route could be found

[dpad85]

The iOS app displays the following message when no route is found:

With additional errors in the details of the payment which are not very understandable ("Payment fee was below the minimum required by the trampoline node").

We should improve that message. Maybe something like: Recipient is not reachable, or does not have enough capacity.

Once the app is able to increase the fee allocated to payments, we should also add a button to bump those fee and retry the payment.