* yg scripts set reloffer/absoffer only:
Prior to this commit, the yield generator user
level scripts required the user to specify offer
types depending on the wallet, but only 'rel/abs'
distinction is user choice; the other element
(native segwit, p2sh or p2pkh) must be defined
by the wallet, so we now call `wallet.get_txtype()`
to translate from reloffer/absoffer to sw0.. etc.
* Taker chooses nversion, nlocktime per wallet type:
Takers who are still using p2sh-p2wpkh wallets will
not want to flag their transactions with different
tx metadata than previous versions that are still
running, so we check the `get_txtype()` output to
decide which nVersion and nLockTime to use.
Also, the SNICKER locktime is reverted to zero as
according to draft spec.
* change offer type in test_coinjoin
* update docs for bech32 wallets
Adam Gibson
chris-belcher