Create lamassu-transactions-csv

Exports contents of postgres transactions table to .csv, encrypts with user's PGP key, sends to email address.

**Dependencies:**
- postfix
- mutt
- software-properties-common (?)
- python-software-properties (?)

**Lacks:**
- Install script for above dependencies and importation of PGP key (probably should be part of https://github.com/lamassu/lamassu-install/blob/master/install, with PGP import optional)
- Calculation of commission earned in fiat at time of transaction (should be part of https://github.com/lamassu/lamassu-server/blob/master/lib/postgresql_interface.js)
- Relative path for transactions-*.csv file