Make nodegit a dev dependency, hidden behind a config flag

Loading nodegit in every build is really slow, when we don't really use it in any real instance because we operate from inside a spotlight instance as a submodule.

Adding it as a dev dependency allows it to be available when running locally, but not incuded as part of the build process.
Set window size to desktop display dimensions

Some tests were failing because the default window dimensions cause the site to display in "mobile" format, truncating some elements and causing tests to fail.
Add tests for journey module
Refactorlooped tests to use new `each` helper instead of `Q.all`
Merge pull request #35 from alphagov/enhancement/load-nodegit-as-dev-dep

Make nodegit a dev dependency, hidden behind a config flag
Added list module tests
Moved "has a title test" to generic module test file
Merge pull request #36 from alphagov/feature/list-module

Feature/list module
Merge pull request #37 from alphagov/feature/journey-module

Feature/journey module
Always test for presence of lines in grouped timeseries
Added tests for completion rate and completion numbers modules
Moved defaulting of module.axes to defaults
Removed x-axis test because it wasn't compatible with pinned start dates
Be cleverer with determining the period text content if start-at is defined in module config
Remove test for student finance which fails on %-ages > 100
Merge pull request #34 from alphagov/feature/completion-rate-module

Feature/completion rate module
Redunant commas are redundant
Merge pull request #38 from alphagov/bugfix/bens-regex-fail

Redundant commas are redundant
Add option to take screenshots of each dashboard

Add a `--screenshot` option which will make a screenshot of each dashboard once it loads, in the dir specified.
Add a screenshot helper in WD which is useful for debugging.