New command line tool to initialise configuration

[davidorme]

It would be cleaner if users could do something like:

safedata_config --init_user
safedata_config --init_site
safedata_config --init /specific/path/config.cfg

And end up with an initial configuration file with default values or gaps to fill in. This should probably be automatically generated from the CONFIGSPEC definition somehow: maybe see DiffSK/configobj#102. We'd need to do something about providing 'placeholder' defaults for all values, I think?

Maybe we could even link that into the taxondb tools to populate the file when they run?