[feature] Allow newly uploaded emojis to be placed in categories (#939)

* [feature] Add emoji categories GET
Serialize emojis in appropriate categories; make it possible to get categories via the admin API

* [feature] Create (or use existing) category for new emoji uploads

* fix lint issue

* update misleading line in swagger docs

testrig/db.go

@@ -55,6 +55,7 @@ var testModels = []interface{}{
 	&gtsmodel.RouterSession{},
 	&gtsmodel.Token{},
 	&gtsmodel.Client{},
+	&gtsmodel.EmojiCategory{},
 	&gtsmodel.Tombstone{},
 }
 
@@ -199,6 +200,12 @@ func StandardDBSetup(db db.DB, accounts map[string]*gtsmodel.Account) {
 		}
 	}
 
+	for _, v := range NewTestEmojiCategories() {
+		if err := db.Put(ctx, v); err != nil {
+			log.Panic(err)
+		}
+	}
+
 	for _, v := range NewTestStatusToEmojis() {
 		if err := db.Put(ctx, v); err != nil {
 			log.Panic(err)