Find some more speed improvements in XPCS:
	1. Move the cpu path to FFTW, if present (factor of 2 faster!)
	2. Manage transfers better on GPU code path (requires 2 new kernels)
	3. Improve the normalization in g2 by pre-computing the reciprocal of the time average, then multiplying instead of dividing. Division is expensive!

I also rewrote lots of g2_numerator to make the calculation easier to understand and better align the cpu and gpu code paths
Add the demo_server script, which does not accept uploads and can be run open to the internet. In the backends, make a modification to the way file uploads are handled to allow for the demo_server mechanism.
Updated readme.txt for web apps