Data layer restructuring (#997)

* Move query builders to sqlite package
* Add transaction system
* Wrap model resolvers in transaction
* Add error return value for StringSliceToIntSlice
* Update/refactor mutation resolvers
* Convert query builders
* Remove unused join types
* Add stash id unit tests
* Use WAL journal mode

pkg/models/model_image.go

@@ -46,3 +46,13 @@ type ImageFileType struct {
 	Width  *int `graphql:"width" json:"width"`
 	Height *int `graphql:"height" json:"height"`
 }
+
+type Images []*Image
+
+func (i *Images) Append(o interface{}) {
+	*i = append(*i, o.(*Image))
+}
+
+func (i *Images) New() interface{} {
+	return &Image{}
+}