extend SauceBrowser init_conf with capabilities supplied in .zuul.yml
test for capabilities
User configurable localtunnel server URL
Merge branch 'capabilities' of https://github.com/phated/zuul
history: add missing entries
Fixes 'latest' keyword not always returning highest available version

The list of available versions is not always ordered, meaning `latest`
just taking the last element of the list doesn't result in the truly
latest browser in all cases.
Adds the ability to specify Firefox extensions to load

Extensions are specified in the firefox_profile field in .zuul.yml by
providing a list of paths to either XPI files or the unpacked extensions.

Style fixes
Merge pull request #60 from minuteman3/firefox-extensions

Adds the ability to specify Firefox extensions to load
Merge pull request #62 from minuteman3/fix-latest-keyword

Fixes 'latest' keyword not always returning highest available version