Merge pull request #312 from rofl0r/help-fix2

fix help text when invoked with --help
Merge pull request #311 from rofl0r/master

fix error to create a wallet due to missing pick_random_server decl
make it possible to create wallet non-interactively

closes #308

additionally it fixes the bug that the default fee and gap limit
were not stored in the new wallet, if entered manually.