The new option is not active yet.

The sources can be registered (as entry_points) in some arbitrary
module available at runtime. We register some modules ourselves,
'system' for starters.

Yet we do not make use of the registered sources in main(). This
will be the next step.

Based on suggestions of @drebs we now start to support different
sources of randomness. We start with one source, the default,
which will be the standard libs `random.SystemRandom` source
we used anyway. But from now on this source if put into a
separate class, tested and all that, which will be registered
as an entry point.

Yet we do not register or work with the registered sources. This
will come next.

We now use an `argparser` options instance for get_passphrase
instead of a bunch of single args. This makes the main function
`get_passphrase` less readable (you do not see immediately what
options are really expected), but avoids misleading defaults. We
now use the defaults set in argparser options, i.e. from
`handle_options()` as single source of defaults.

Move wordlists into the new package. This should fix
the data_files problem on most platforms and in most
environments.

Seems to be really tricky to install data files in a
foreseeable location.

The more finegrained solution of conorsch might be
slightly less stable in the long run, therefore we
selected the 'package', actually.