PROV-1083 Added custom extension of doctrine file system cache

This should give us more multi-platform friendly file names for on-disk
caching and we don't have to impose any restrictions on cache keys.
Merge branch 'develop' of github.com:collectiveaccess/providence into develop

* 'develop' of github.com:collectiveaccess/providence:
  PROV-1082 basic ULAN importer