Redis integration for caching and lookup of docid's.
Access via RecordIdentifier implemented.

Format
type:recordIdentifier, e.g. "gbv-ppn:PPN513009361_0025"
Cleanup - removed unused code.
Identification via primary identifier and no longer ia mongoDB docid's.

If a purl is present this is used. Format:    purl:hash:<hash_of_purl>
Otherwise, if a gbv-ppn is present the id is: gbv-ppn:hash:<hash_of_gbv-ppn>
Otherwise, if a ppn is present the id is:     ppn:hash:<hash_of_ppn>

More Mappings could be implemented in the method: DocService.getPrimaryId(..)
getPrimaryId modified. Type "ppn" added.
Wrong mets-Url fixed.
Comment out caching.
Merge branch 'master' of https://github.com/subugoe/Meta-Data-Access-Service