Streamline QA tools

- Remove coveralls (service does not work)
- Replace check-cs.sh with inline `--config-file` option for php-cs-fixer
- Remove psr0 rule for php-cs-fixer (we use psr4)
- Add contribution guide
CS fixes (unused use statements)
Merge branch 'feature/streamline-tools'

Streamline QA tools; add contribution guide