make it possible to create wallet non-interactively

add a --password option,
respect --server,--fee,--gap as passed on the command line,
and do not ask for them if they were specified.

so if all of them are passed, there are no interactive questions
asked and one can create wallets automatically via scripts.

closes #308

additionally it fixes the bug that the default fee and gap limit
were not stored in the new wallet, if entered manually.

additionally it fixes the bug that the wallet path was not displayed
correctly if a custom wallet path was used.