Add initial avatar support

We change the code for dealing with contacts quite significantly,
adding a new class, CallsBestMatch, in order to encapsulate a lot of
the functionality that was in CallsCallRecordRow.

At present avatars are not rounded and there are no auto-generated
avatars for contacts with no avatar.  This work is awaiting discussion
of Apps_Issues#164.

src/calls-best-match.h

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2019 Purism SPC
+ *
+ * This file is part of Calls.
+ *
+ * Calls 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.
+ *
+ * Calls 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 Calls.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Bob Ham <bob.ham@puri.sm>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ */
+
+#ifndef CALLS_BEST_MATCH_H__
+#define CALLS_BEST_MATCH_H__
+
+#include "calls-vala.h"
+
+#include <gdk/gdk.h>
+
+G_BEGIN_DECLS
+
+#define CALLS_TYPE_BEST_MATCH (calls_best_match_get_type ())
+
+G_DECLARE_FINAL_TYPE (CallsBestMatch, calls_best_match, CALLS, BEST_MATCH, GObject);
+
+CallsBestMatch  *calls_best_match_new            (CallsBestMatchView *view);
+const gchar *    calls_best_match_get_name       (CallsBestMatch     *self);
+GdkPixbuf *      calls_best_match_request_avatar (CallsBestMatch     *self,
+                                                  gint                size);
+
+G_END_DECLS
+
+#endif /* CALLS_BEST_MATCH_H__ */