Reorganise cucumber features

The following features better reflect the scenarios we've got now:

- admin
- backdrop_read
- backdrop_write
- spotlight_assets
- stagecraft
Rename feature `admin` to `admin_uploader`
Merge pull request #12 from alphagov/reorganise-features

Reorganise cucumber features
Ignore pyc files
Adds a script to check smokey JSON for a feature

Given a JSON output file from Smokey (`cucumber --format json`) and a
feature name this script will print out a report of that feature's run
and return an exit status; 0 if there were no failures 2 if there were
failures.

This is similar to the script in alphagov/smokey but a bit simpler. It
doesn't log or report on a couple of failures that it should.
Make check.py executable, fix PEP8 errors
Add a wrapper script to check a named feature

For a given test name, run the JSON results parser and return an
error code that will be understood by Sensu.

It downloads the `results.json` file from the `pp-smokey` Jenkins job
artifact.

Example:
```
check_feature.sh backdrop_write
```

Would download the results of the last Jenkins pp-smokey run, parse the
JSON file and return 0 for success and nonzero for failure.
Make Jenkins output a results.json file

We can then use this as a build artifact. Sensu checks can download and
parse this.

Had to change the way we run from `bundle exec rake` to `bundle exec
cucumber` in order to pass arguments to cucumber.