authorids: models addition

* Adds models for aidDENSEINDEX and aidINVERTEDLISTS tables.
  Addresses #1790.

* Refactors the indentations.

Signed-off-by: Mateusz Susik <mateuszsusik@gmail.com>
authorlist: initial release

* Adds new module inside /invenio/invenio/modules for authorlist

* Adds SQLAlchemy models for 6 new tables. Fixes #1891.

Signed-off-by: Mateusz Susik <mateuszsusik@gmail.com>