[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

internal/processing/admin/getcategories.go

@@ -0,0 +1,47 @@
+/*
+   GoToSocial
+   Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Affero General Public License as published by
+   the Free Software Foundation, either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package admin
+
+import (
+	"context"
+	"fmt"
+
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+)
+
+func (p *processor) EmojiCategoriesGet(ctx context.Context) ([]*apimodel.EmojiCategory, gtserror.WithCode) {
+	categories, err := p.db.GetEmojiCategories(ctx)
+	if err != nil {
+		err := fmt.Errorf("EmojiCategoriesGet: db error: %s", err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	apiCategories := make([]*apimodel.EmojiCategory, 0, len(categories))
+	for _, category := range categories {
+		apiCategory, err := p.tc.EmojiCategoryToAPIEmojiCategory(ctx, category)
+		if err != nil {
+			err := fmt.Errorf("EmojiCategoriesGet: error converting emoji category to api emoji category: %s", err)
+			return nil, gtserror.NewErrorInternalError(err)
+		}
+		apiCategories = append(apiCategories, apiCategory)
+	}
+
+	return apiCategories, nil
+}