Added Postgres tables for coverage model.
Adding table definitions for coverage_model.
Changed package/path for coverage data store
Added indexes for coverage_spans table.
Switched from geography column to geometry column to increase precision.
Merge branch 'master' of https://github.com/ooici/ion-definitions into HDFtoDB
Merge branch 'HDFtoDB' of git://github.com/caseybryant/ion-definitions into HDFtoDB
Merge pull request #516 from caseybryant/HDFtoDB

M114: Add Postgres table definitions for coverage-model