Fix gratipay.version when Git is not installed

Python raises OSError in this case. The fact is missing from check_output docs https://docs.python.org/2/library/subprocess.html#subprocess.check_output
version: Do not fail on git version check
Simplify version handling

See https://github.com/gratipay/gratipay.com/pull/2905 for discussion
Remove rsa dependency, which is not needed (fixes #1834)

We don't use it directly and dependent libraries are coded
to use pycrypto if it is available.
Remove rsa from requirements.txt
Start rewriting Vagrantfile for Ubuntu 14.04 (#2327 and #2868)
vagrant: Install PostgreSQL
vagrant: Comments and minor fixes
virtualenv: Do not symlink, because shared folders may not support them
vagrant: Add scripts/vagrant-debian.sh for system prerequisites
vagrant: Run scripts/vagrant-setup.sh for basebox
vagrant: Simplify scripts/vagrant-setup.sh

Windows Git doesn't mess with newlines by default anymore, so remove
that warning. Modify `/etc/profile.d` with sudo, demystify PostreSQL
command line.
Add helper for JS tests
vagrant: Merge db init .sql scripts in to reset-db.sql

This makes reprovisioning idempotent.
vagrant: Create vagrant role for PostreSQL and use that to access DB
Fix #2950 - fake_data generates 0.00 transfers that break positive constraint
Remove stray comments from gratipay/version.py
Switch from Dalek.js to webdriver.io
Add one authed test.
Use phantomjs instead of Chrome.  Should make Travis happy