Remove gems with no direct requirement / no longer in use.

N.B. Heroku no longer advise using therubyracer https://devcenter.heroku.com/articles/rails-asset-pipeline#therubyracer

Signed-off-by: Tom Anderson <toanderson@pivotal.io>
retire xpath gem to reduce dependencies

Signed-off-by: Tom Anderson <toanderson@pivotal.io>
retire ffaker gem and use factorygirl sequences, to reduce dependencies

Signed-off-by: Tom Anderson <toanderson@pivotal.io>
retire dynamic_form gem and use helper method display error messages to end-user

Signed-off-by: Tom Anderson <toanderson@pivotal.io>
remove memcached documentation references and dalli gem, as memcached is not in use. Fixes #60.

Signed-off-by: Tom Anderson <toanderson@pivotal.io>