SPI rework

Reviewed package structure and API vs SPI problems.

 - https://hibernate.atlassian.net/browse/HSEARCH-1673
 - https://hibernate.atlassian.net/browse/HSEARCH-1730
 - https://hibernate.atlassian.net/browse/HSEARCH-1739
 - https://hibernate.atlassian.net/browse/HSEARCH-1740

If the thing is builds is _SearchIntegrator_ why is this then a _SearchIntegrationBuilder_  instead of a _SearchIntegratorBuilder_