CQEngine, ElasticSearch, MongoDB and Hazelcast as optional dependencies.

[codingchili]

• [x] move :storage:elastic into :core
• [x] document how to exclude optional dependencies
• [x] document which dependencies that are optional
• [x] make sure to not reference optional dependencies from core features.

[codingchili]

Document the reduction in JAR size for each.

[codingchili]

Waiting for tests 9537bdd6a12e897960ca6d6f1e44c5c662ecefbd

[codingchili]

Tests passed.