Install the NG version of the health_manager.

While here, let's clean up a few loose ends.
Cleanup: we don't really depend on the cloud_controller anymore.
Cleanup: the health_manager does not connect to the PostgresSQL DB anymore.
Cleanup: the health_manager does not connect to the PostgresSQL DB anymore; remove that from documentation too.
Cleanup: the health_manager does not connect to the PostgresSQL DB anymore; remove that from tests too.
Cleanup: bring file more in line with upstream (even if for now we hardcode the index).
Cleanup existing intervals attributes pending more changes.
Cleanup: reindent in preparation for more changes.
Cleanup: reindent in preparation for more changes.
Update intervals for HM next: add new ones, fix a typo, update default values.
Configure the URL to the cloud_controller.
Cleanup: update documentation for tunable settings.
Cleanup: reindent and slightly reword some existing documentation.
Finish documenting all tunables.
Bump reference to pick up a few bug fixes.
Release 2.0.0: deploy "HM next".