core: add plannerShared class

Add a plannerShared class, whose purpose is to contain shared
functions between mobile and desktop

This class is the inner workings of the diveplanner not the UI

Signed-off-by: Jan Iversen <jan@casacondor.com>

core/plannershared.cpp

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "plannershared.h"
+
+
+plannerShared *plannerShared::instance()
+{
+    static plannerShared *self = new plannerShared;
+    return self;
+}