Feat/bitcoin logic

I kinda cheated for our MVP. Rather than a multi-signature wallet, it splits the single key in half. The idea is the same, you can’t spend anything in the wallet until you have the full key. Working on the multi-signature wallet, but there’s more complicated logic that I have to wrap my head around first.

- To do: 
- Right now the logic lies in a utilities file. I need to figure out where exactly I will use this logic (in routes.js in response to a GET request? in server.js?) and add it there
- Find a way to save key fragments + addresses to the database (associated with a user)
- I also wrote tests for this; I’ll try to add them to the gulp ’test’ task soon.