Extend .gitignore for Erlang and Emacs
Add postgresql integration and initial contract handling

* Add epgsql and poolboy deps
* Add poolboy worker callback module and supervisor
* Add initial poolboy postgresql configs in app module
* Add enter-contract JSON API
* Add contract handling module with enter-contract API validation
* Add initial modules for Postgres handling
* Add Postgres bootstrap scripts
* Add jiffy as dep for JSON decoding
Merge branch 'features/api2_and_postgres'

* features/api2_and_postgres:
  Add postgresql integration and initial contract handling
  Extend .gitignore for Erlang and Emacs