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)
- Added contribution guide
CS fixes

- Unused use statement
Merge branch 'feature/streamline-tools'

Streamline QA tools and add contribution guide