Create program to rescale dark file

[benj]

We need a program that will read in a dark frame file, rescale it to mimic that for a different integration time and then output the new file.

Basic level: Read in data file, multiply by a user-specified scaling factor (except pixels 1 & 2 on band 1 for each line), output new data file.

What we really want: Same, but calculate scaling factor from differential of integration times - check relative data values for existing dark files to try and work out if the result of changing the integration time is just a linear scaling (hopefully) or something more complicated, then implement appropriate algorithm. The user should also be able to specify a scaling factor as above if they prefer.

Gold-plated: Same, but also account for changes in framerate and in spectral/spatial binning. May be worth spending half an hour to check whether the effects of altering these are also just linear scaling, but if they're not then don't include them (assume constant).