Adds individual activity render.
Fixes sinatra/tilt version issue.

Interestingly bundler is deciding that 1.0 is the newest sinatra version
despite it being 4 years old. Probably because that was in their
non-semver period and it is just 3 characters vs. '1.4.3' ? No matter,
it is fixed with a version specifier in the gemspec, which should be
harmless.
Adds individual activity render in json/xml.