Review Indexes creation and manipulation in AtomDB

[andre-senna]

EPIC

• Review unit and integration AtomDB tests das-atom-db#203
• Review unit and integration QE tests das-query-engine#330
• Simplify Patterns das-atom-db#204
• Custom patterns index schema das-atom-db#205

Detailment:

• Review unit and integration tests
  • Create new test cases to cover more special cases
  • Improve testing infrastructure (better mocks, stubs, shared data schemas, etc)
  • (when applicable) Improve the way current test cases are being performed
• Simplify Patterns (and other similar) index to store Handle -> Set of mathcing handles instead of Handle -> Pair(Handle, List of Handles) as we have now.
• To define and implement a way to allow users to determine how patterns are created given a newly inserted link in order to populate the patterns's index