Integrating support for graphene-sqlalchemy-filter into code base

As there is limited filtering with graphene-sqlalchemy, I have been using graphene-sqlalchemy-filter which has many stock filters included. Unfortunately the developer seems to have lost interest in the code base and a critical PR to add support for Graphene 3.0 has been unmerged for six months.

• https://github.com/art1415926535/graphene-sqlalchemy-filter/pull/63

I have tried contacting the developer a few times without response.

As the filtering code for the add-on is contained in the graphene-sqlalchemy-filter package's two files, I propose merging this code into graphene-sqlalchemy.

Would this be OK?