Code formatting

[inyono]

This PR adds code formatters for most of the languages used in the projects (except Twig since I didn't find a good code formatter).

Please code review

• 42bf904
• fac3427

and scan b708849 to check if you are okay with coding changes introduced by php-cs-fixer.

Changelog

Added

• Add package.json so that we can use yarn as task runner
• Add yarn script start that executes docker-compose up
• Add yarn script format:prettier that executes prettier (formats Markdown, YAML, JSON, etc.)
• Add yarn script format:php that executes php-cs-fixer (formats PHP according to PSR-2 with some additional rules)

TODO

• Update changelog
• Add yarn lint that checks if files are formatted according to prettier / php-cs-fixer config
• Execute yarn lint in CI

[inyono]

@Knorrke Apart from the CI / lint stuff, this is done now

[Knorrke]

Code looks great, do you want to fix the failing travis builds before merge?