Add support for custom ssb path

[stripedpajamas]

This should allow stuff like running from a USB stick (#822). I added commander as a dependency so other command line options could be added later if the need arises.

With this PR, someone could set their shortcut to something like patchwork --path /custom/path or even patchwork --path . to use the cwd, which should be perfect for portable installs.

Since git-ssb doesn't take in configs, I have Patchwork skip starting it up if a custom path was passed in. If git-ssb changes to allow more granular configs, we can take that conditional out.

[mmckegg]

@stripedpajamas

This looks pretty good, and I'm tempted to accept as is. The only issue I have is that ssb-config actually has it's own command line parser (minimist via rc which is clever, but I'm not a huge fan of) that that takes the args passed to patchwork and turns them into config automatically.

So passing --path SOMETHING to patchwork would actually already set config.path: "SOMETHING". You can also do things like --friends.hops 10 which would set config.friends.hops.

It might be worth having a play around with the built in arg parser and see if you can get it do what you want. If not, I'll merge this!

[stripedpajamas]

Nice catch!! It works perfectly. I updated my PR to just not start git-ssb if a custom path was passed in, so it doesn't blow up.