feat: improve meals with better search and ids (#5)

Features:
- Meals now have an id instead of a title only
- It is now possible to get all meals without date or restaurant filter
- Sorting meals output

Reviewed-on: #5
Co-authored-by: bdoerfchen <git@bissendorf.co>
Co-committed-by: bdoerfchen <git@bissendorf.co>

model/external/stwbremen/meal.go

@@ -2,6 +2,7 @@ package stwbremen
 
 type Meal struct {
 	Title       string       `json:"title"`
+	ID          string       `json:"id"`
 	Ingredients []Ingredient `json:"ingredients"`
 	Prices      []Price      `json:"prices"`
 	Location    string       `json:"location"`