[Kst] [Bug 126641] Should be able to calculate white noise limit

[Barth Netterfield]

> I would like to implement this as a fitting plugin. 

Seems right.  There is a plan to upgrade the API for plugins though.  George: 
what is the scehdule on that.

> The plugin will operate 
> on a power spectrum, fitting for the 1/(f^a) noise and the white noise
> limit at high frequencies. The options will be something like..
>
> - # of points to fit 1/f noise (or a maximum 1/f noise frequency).
> - # of points to fit white noise (or a minimum white noise frequency).
>
> It will produce scalars for the knee frequency, the white noise limit, and
> the fit parameter a.

... and the other standard vectors that other fits produce (the fit, error, 
etc).

> It will produce a plot with the original power spectrum, a fit curve which
> shows the intersection of the white noise limit with the 1/f noise, and
> labels containing the values of the calculated scalars.

Look at how other fits currently work (in a plot->rmb->fit... etc).  This 
should work the same way.