Allow adding scopes to HasMany fieldtype

[mxaGianluca]

It would be great if you can add a scope to a HasMany relation. This would allow you to configure how the same relation behaves depending on where you use it.

Right now you have the option to add a scope for the runwayListing by defining a scopeRunwayListing on the model. But i think it would be really handy to be able to add a scope when you configure the relation in the cp.

[duncanmcclean]

Statamic's built-in Entries fieldtype has a "Query Scopes" config option. I'd accept a PR adding the same option to Runway's Belongs To & Has Many fieldtypes.