in conmock, options.param gets passed as 4th arg for handler.

This allows us to test handlers for express' app.param().
Added 'badgeUrl' app param, and a stub '/share/badge/:badgeUrl' route.

The route just returns 501 Not Implemented for now.
Added a real /share/badge/:badgeUrl view, rather than a 501.
All client-side templates have 'csrfToken' in their context now.

nunjucks doesn't seem to support the idea of an environment that contains
context globals, like jinja2 for python does, so I added a bit of support
for it. Ideally we would push this upstream rather than hack our use of it,
but WE'VE GOT DEADLINES.
Added a POST /share/badge/:badgeId route and a button in UI to trigger it.
renamed badge#share tests to be more descriptive. added more assertions.
Merge pull request #561 from toolness/badge-sharing

Badge sharing