R2 term response function for Sharpening Deconvolution Transform (SDT)

The original SDTModel and odf_sharp functions assume that the ODF was computed from q-ball imaging. Q-ball imaging computes the ODF integral without the r^2 (r2) term in the integral. So does the response function for deconvolution of a q-ball.

Here, I have re-derived the correct analytical solution for the response function taking into account the r^2 term in the ODF integral. Hence, ODFs coming from models such as DSI, GQI, CSA, Multi-tensor, SHORE, which all derive their ODF using the r2 term should be deconvolved with this new correct analytical response function.

An example will soon follow from @Garyfallidis as part of his ISMRM 2014 work.