NXP-14868: fix repositoryName init; cleanup

Factorize DEFAULT_DIGEST
New methods:
- AbstractBinaryManager.getDigest()
- CachingBinaryManager.initialize(BinaryManagerDescriptor)
- CachingBinaryManager.initializeCache(String, FileStorage)
Cleanup inherited fields useless override
Merge pull request #8 from nuxeo/fix-NXP-14868-init-repositoryName

NXP-14868: fix repositoryName init; cleanup