added versionservice skeleton and removed versionpaths from entity class

fixed unit tests and some integration tests

implemented retrieeve old version method

fixed query for old versions and fixed tests to not check for the non existant versionpaths on the entity anymore

added unit test for versionservice
updated weed fs binary dl link
Merge pull request #3 from fasseg/version-index

Versionservice is now using it's dedicated ElasticSearch index
added an abstract elasticsearch service with urility methods