Bulk update scenes (#92)

* Add bulk update functionality

* Restore multiselect fixes from previous branch

* Prevent unsetting of studios/tags

* Detect when slice fields are omitted and ignore

pkg/api/resolver.go

@@ -5,6 +5,8 @@ import (
 	"sort"
 	"strconv"
 
+	"github.com/99designs/gqlgen/graphql"
+
 	"github.com/stashapp/stash/pkg/models"
 	"github.com/stashapp/stash/pkg/scraper"
 )
@@ -165,3 +167,13 @@ func (r *queryResolver) ScrapeFreeones(ctx context.Context, performer_name strin
 func (r *queryResolver) ScrapeFreeonesPerformerList(ctx context.Context, query string) ([]string, error) {
 	return scraper.GetPerformerNames(query)
 }
+
+// wasFieldIncluded returns true if the given field was included in the request.
+// Slices are unmarshalled to empty slices even if the field was omitted. This
+// method determines if it was omitted altogether.
+func wasFieldIncluded(ctx context.Context, field string) bool {
+	rctx := graphql.GetRequestContext(ctx)
+	
+	_, ret := rctx.Variables[field]
+	return ret
+}