Refactor simulate to split UI from application

Fix name of glew library

Move simulate to new directory and refactor to use C++ conventions

Wrap simulate in mujoco namespace

fix namespaces, convert struct to class, use std::lock_guard

use GetMutex to better handle destruction ordering

rename mjSimulate to Simulate

nit: space before public and typo

move startup print

use nullptr instead of NULL

use GetInstance() to get simulate object

convert init to default constructor

sample/Makefile

@@ -11,6 +11,3 @@ all:
 	$(CXX) $(COMMON) derivative.cc         -lmujoco -fopenmp -o ../bin/derivative
 	$(CXX) $(COMMON) basic.cc              -lmujoco -lglfw   -o ../bin/basic
 	$(CXX) $(COMMON) record.cc             -lmujoco -lglfw   -o ../bin/record
-	$(CC) -c -O2 -I../include uitools.c
-	$(CXX) $(COMMON) uitools.o simulate.cc -lmujoco -lglfw   -o ../bin/simulate
-	rm *.o