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
Upgrade Bitbucket API to 2.0
Adds gettext i18n of %username/members/index
Get HTML tags out of translation strings
Move i18n strings into jinja template
Merge pull request #2921 from gratipay/i18n-team-members

Adds gettext i18n of %username/members/index
Fix giving page for admins
Merge pull request #2924 from gratipay/fix-giving-page-admin-text

Fix giving page for admins
Bring back support for /on/bitbucket/team/
update i18n files
Bump version to 1734
Set up a system for generating the UPDATE
Here's an update.sql for 4,271 accounts
Here's the error log from the update generation

This should be pruned during landing.
Here's a list of the usernames that are truly 404
Here's a couple helper scripts for exploring bb
Here's a little SQL to dump Bitbucket usernames
Here's the bitbucket dump I'm using
Enable the update sql from branch.sql