Move the Ref interface from gui/types to models

This is a type that can be useful for model/backend stuff, so move it there. We
are going to use it in the API of the commit loader.

pkg/gui/types/ref.go

@@ -1,14 +0,0 @@
-package types
-
-type Ref interface {
-	FullRefName() string
-	RefName() string
-	ShortRefName() string
-	ParentRefName() string
-	Description() string
-}
-
-type RefRange struct {
-	From Ref
-	To   Ref
-}

pkg/gui/types/ref_range.go

@@ -0,0 +1,8 @@
+package types
+
+import "github.com/jesseduffield/lazygit/pkg/commands/models"
+
+type RefRange struct {
+	From models.Ref
+	To   models.Ref
+}