add FileCacheManager

Add support for caching information about state of fixing files.
Cache is supported only for phar version and version installed via composer.
 
 File will be processed by PHP CS Fixer only if any of the following conditions is fulfilled:
 * cache is not available,
 * fixer version changed,
 * file is new,
 * file changed.
One more thing.
For big projects one may want to keep .php_cs.cache as repo file (not excluded!).
It will be worthless if contains absolute paths.