Brakeman config added

The rest of the config is in under config dir, which holds
the warnings we know about and which should be ignored
Added Brakeman to the Gemfile

So that you don't have to work out the PATH where brakeman
is installed
Add a script for CI to run.

This means we can change the commands being run per branch, for instance
to run brakeman on this branch but not others until this PR is
merged
Added ci_reporter gem to Gemfile

The idea is to have a gem that is required for CI be installable
via bundler rather than embedding the full path to it, which
contains the gem's version in the path name, which will change
in the future.
Merge pull request #45 from ministryofjustice/brakeman

Brakeman config added