Move provider plugins into a dedicated directory

Since we will introduce another type of plugin for the policy engine
we want to have each plugin type in separate directories.

We also have to adjust:

- plugin search directories
- po file location
- update paths for calls-doc target

plugins/provider/sip/calls-sip-account-widget.h

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2021 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: Evangelos Ribeiro Tzaras <evangelos.tzaras@puri.sm>
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *
+ */
+
+#pragma once
+
+#include "calls-sip-provider.h"
+
+#include <handy.h>
+
+G_BEGIN_DECLS
+
+#define CALLS_TYPE_SIP_ACCOUNT_WIDGET (calls_sip_account_widget_get_type ())
+
+G_DECLARE_FINAL_TYPE (CallsSipAccountWidget, calls_sip_account_widget, CALLS, SIP_ACCOUNT_WIDGET, GtkBox)
+
+CallsSipAccountWidget *calls_sip_account_widget_new           (CallsSipProvider      *provider);
+void            calls_sip_account_widget_set_origin    (CallsSipAccountWidget *self,
+                                                        CallsSipOrigin        *origin);
+CallsSipOrigin *calls_sip_account_widget_get_origin    (CallsSipAccountWidget *self);
+
+G_END_DECLS