Faucet doesn't work with sapling addresses

[garethtdavies]

As there is a check of the length of the address the faucet only recognises Sprout addresses and so won't work with Sapling addresses see https://github.com/zcash/zfaucet/blob/master/faucet/views.py#L78

In addition to the above, even if it did detect Sapling addresses correctly it would likely hit an issue sending from a Sprout address to a Sapling one (or vice versa) directly as it is just using the first returned address from z_listaddresses.

A suggested hacky quick fix could look something like the following garethtdavies/zcash-faucet@ffbfffc where transparent addresses are used to send Sapling txs to keep existing support for Sprout txs. This is utterly untested and uses this method https://github.com/arcalinea/pyZcash/blob/master/pyZcash/rpc/ZDaemon.py#L93 to get the sending t-addr as the existing transparent stuff doesn't use z_sendmany so doesn't have this issue.

A better fix would involve invoking z_validateaddress to detect Sapling/Sprout addresses and selecting the sending address appropriately.

[garethtdavies]

Just updating this. The reason I didn't make a PR and test the above is that I ran into some issues during the setup (I can't recall what exactly). If anyone wants to get this into a working Docker container(s) that'd be awesome 👍