Switch out Cucumber for Spinach

Spinach seems like a much nicer solution - steps are well defined and in
obvious places. This is mostly a straight conversion, although I have reworked
some of the tests - the main change being 'am on' -> 'visit' for URLs.

While doing this, I noticed a few features that have multiple steps where not
really needed - a 'submit form with data' rather than 'fill in form' and
'submit' would be much easier to read (and less code)
Generally change 'fill in' and 'submit' with 'submit with'

Reduces the number of steps in each feature and makes them more readable
Strip out wrapper for travis rake task - just call tasks directly

I think we could have done this when we moved away from cucumber
Run travis task with --trace
Specify spinach and rspec in Gemfile as test gems

Should (hopefully) make versioning slightly easier
Set RSpec environment within spec_helper

This is what the rake task was doing before. Might as well set it in the helper
file. Also removed the env setting from the Guardfile
Re-add coveralls support

This *should* merge results in from Spinach and RSpec. Previously we had to use
a workaround
Merge pull request #5 from thomas-mcdonald/spinach

Convert Cucumber specs to Spinach