Use subgraph clusters for vertex groups
Only add vertex labels when needed
Use php-cs-fixer to adopt PSR-2 code style
Add whitespace around operators
Remove trailing whitespace from each line
Consistently use single quotes
Add whitspace between concatenations
Align all comments consistently
Run php-cs-fixer once again
Merge branch 'graphviz-cluster'

Conflicts:
	lib/Fhaculty/Graph/GraphViz.php