Updates support@gittip.com to support@gratipay.com

Fixes #2698
allow admins to rename user accounts
return a 403 instead of redirecting
fix tests
fix overflow of Sign In buttons
fix overflow of age
reduce font size in a couple of places
trailing_zeroes option added to format_currency, defaults to true
Removed trailing zeroes on support-gratipay banner
fix code style
simplify
go back to a simple `.replace()`
don't show trailing zeroes for user goals
don't show trailing zeroes for tip amount suggestions
Update Google site verification

This is for Google Apps and maybe Google Plus? Necessary because of the
rename to Gratipay.
Merge pull request #2717 from gratipay/google-verification

update Google site verification
Bump version to 16.0.3
Bump version to 16.0.3-dev
Merge pull request #2714 from gratipay/fix-trailing-zeroes-2683

Fix trailing zeroes (#2683)
Merge pull request #2715 from gratipay/fix-overflows

Fix overflows