search: Introduce a search engine

This is architectured in such a way that it will
allow us to introduce other searcheable terms in
the future.

All the functionality that in the past was in
GcalManager is now spread across GcalSearchModel,
GcalSearchHitEvent and GcalSearchEngine.

src/search/gcal-search-model.h

@@ -0,0 +1,33 @@
+/* gcal-search-model.h
+ *
+ * Copyright 2019 Georges Basile Stavracas Neto <georges.stavracas@gmail.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#pragma once
+
+#include <gio/gio.h>
+
+G_BEGIN_DECLS
+
+#define GCAL_TYPE_SEARCH_MODEL (gcal_search_model_get_type())
+G_DECLARE_FINAL_TYPE (GcalSearchModel, gcal_search_model, GCAL, SEARCH_MODEL, GObject)
+
+GcalSearchModel*     gcal_search_model_new                       (GCancellable       *cancellable,
+                                                                  gint                max_results);
+
+G_END_DECLS