Require spree assets so that Spree variable is available in admin tests
Require correct poltergeist path
Use correct coffee-rails and sass-rails gems
Try to save us from db locking in spec runs.

- Bumped database cleaner to 1.2.0
- Change spec strategy for how it runs.

This due to that I got random failed spec runs due to random table
locking SQLite3::BusyException: database is locked

Conflicts:
	spec/spec_helper.rb

Fixes #93