IDA: Use SortXAxis in MSDFit and ElWin

[mantid-builder]

Original Reporter: Samuel Jackson

There are a couple of places where we are manually flipping the x axis so it is in increasing order. I think we can probably replace those bits of code with the SortXAxis algorithm

For example, line ~299 in IndirectDataAnalysis.py:

#!python
    if(datTx[0] > datTx[-1]):
        # if so reverse data to follow natural ordering
        datTx = datTx[::-1]
        datTy = datTy[::-1]
        datTe = datTe[::-1]

[mantid-builder]

This issue was originally trac ticket 9985