Add Mrntt component; init globalMind in mrntt.initializeReq

This makes the initialization sequence much cleaner and conceptually
well encapsulated.

We also now dynamically allocate the Mind objects. They're allocated
dynamically by Mrntt inside of initializeReq. This means that we no
longer have to worry about jolting and cleaning up the running threads
of global mind object even when we never explicitly called
Mind.initializeReq.

Along with other conceptual improvements to our abstractions, this
patch also gets us to a real "end of program initialization" point
for the first time.

include/config.h.in

@@ -9,6 +9,9 @@
 #define CONFIG_MIND_VOSCILLATOR_PERIOD_MS @MIND_VOSCILLATOR_PERIOD_MS@
 #define CONFIG_MIND_VOSCILLATOR_FREQ_MS @MIND_VOSCILLATOR_FREQ_MS@
 
+/* World thread configuration */
+#cmakedefine WORLD_USE_BODY_THREAD
+
 /* Cross-compilation configuration */
 #cmakedefine CMAKE_CROSSCOMPILING