support paying to p2wkh addresses

[Roasbeef]

The "Pay" screen atm will reject a p2wkh address (looks like tb1q94yln7u75nt580a6s0gvs9wqvmfl4zgcxj78sw on testnet). I think this is just an issue with the client side regex validation. It should be updated to accept the base32 character space that bech32 uses.

[tanx]

@Roasbeef good catch