NXP-14868: fix repositoryName init; cleanup

https://jira.nuxeo.com/browse/NXP-14868 - Cleanup CachingBinaryManager implementations and fix repositoryName init

Other important changes are in:
- nuxeo/nuxeo-core-binarymanager-jclouds#1
- nuxeo/nuxeo-core-binarymanager-s3#1 
- nuxeo/nuxeo-core-binarymanager-sql#1

Factorize DEFAULT_DIGEST
New methods:
- AbstractBinaryManager.getDigest()
- CachingBinaryManager.initialize(BinaryManagerDescriptor)
- CachingBinaryManager.initializeCache(String, FileStorage)
Cleanup inherited fields useless override