add FacetWP integration

[macbookandrew]

This adds FacetWP integration for all configured MB Relationships.

Here is a screenshot of the FacetWP settings showing all configured relationships available as data sources:

Would you like to add it in this plugin, or would you prefer to add it to https://github.com/wpmetabox/meta-box-facetwp-integrator instead?

[rilwis]

Hi @macbookandrew ,

Thanks a lot for your help! I think it's best to add it to the https://github.com/wpmetabox/meta-box-facetwp-integrator, because it's where all the integration is. Would you mind moving the code over there?

[macbookandrew]

Moved to wpmetabox/meta-box-facetwp-integrator#2