Streamline QA tools

- Removed coveralls (service does not work)
- Replaced check-cs.sh with inline `--config-file` flag for php-cs-fixer
- Removed psr0 rule for php-cs-fixer (we use psr4)
- Added contribution guide
CS fixes (trailing whitespace, unused use statement)
Merge branch 'feature/streamline-tools'

Streamline QA tools; add contribution guide