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/version.c

@@ -0,0 +1,18 @@
+#include "ssrf-version.h"
+
+const char *subsurface_git_version(void)
+{
+	return GIT_VERSION_STRING;
+}
+
+const char *subsurface_canonical_version(void)
+{
+	return CANONICAL_VERSION_STRING;
+}
+
+#ifdef SUBSURFACE_MOBILE
+const char *subsurface_mobile_version(void)
+{
+	return MOBILE_VERSION_STRING;
+}
+#endif