introduce WorkoutItem, refactor ExerciseTemplate to Exercise

WorkoutsPlus/Exercise/AddExercise.swift

@@ -11,16 +11,16 @@ struct AddExercise: View {
 		@Environment(\.modelContext) private var modelContext
 		@Environment(\.dismiss) private var dismiss
 		
-		@Bindable var exerciseTemplate: ExerciseTemplate
+		@Bindable var exercise: Exercise
 		
 		var body : some View {
 				Form {
-						TextField("Workout Name", text: $exerciseTemplate.name)
+						TextField("Workout Name", text: $exercise.name)
 				}
 				.toolbar {
 						ToolbarItem(placement: .cancellationAction) {
 								Button("Cancel") {
-										modelContext.delete(exerciseTemplate)
+										modelContext.delete(exercise)
 										dismiss()
 								}
 						}
@@ -36,6 +36,6 @@ struct AddExercise: View {
 #Preview {
 		Color.clear
 				.sheet(isPresented: .constant(true)) {
-						AddExercise(exerciseTemplate: ExerciseTemplate(""))
+						AddExercise(exercise: Exercise(""))
 				}
 }