Move subsurface-core to core and qt-mobile to mobile-widgets

Having subsurface-core as a directory name really messes with
autocomplete and is obviously redundant. Simmilarly, qt-mobile caused an
autocomplete conflict and also was inconsistent with the desktop-widget
name for the directory containing the "other" UI.

And while cleaning up the resulting change in the path name for include
files, I decided to clean up those even more to make them consistent
overall.

This could have been handled in more commits, but since this requires a
make clean before the build, it seemed more sensible to do it all in one.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

core/device.h

@@ -0,0 +1,18 @@
+#ifndef DEVICE_H
+#define DEVICE_H
+
+#ifdef __cplusplus
+#include "dive.h"
+extern "C" {
+#endif
+
+extern struct divecomputer *fake_dc(struct divecomputer *dc, bool alloc);
+extern void create_device_node(const char *model, uint32_t deviceid, const char *serial, const char *firmware, const char *nickname);
+extern void call_for_each_dc(void *f, void (*callback)(void *, const char *, uint32_t,
+						       const char *, const char *, const char *), bool select_only);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // DEVICE_H