Major update of X-Ray Attenuation Calculator

I just updated the X-Ray Attenuation Calculator, to also include the NIST database of compounds. Besides, the graph engine has been update to the latest achartengine, which was published a few days ago. This version of achartengine should be compatible with android 1.5 and 1.6 again, so if requested I will change the app to be available for those android versions too.