T1 acquisition orders

[alexdaniel654]

Currently ukat only supports ascending slice acquisition orders i.e. ukat assumes the zeroth slice was acquired first, next slice tss later, the next slice 2 x tss later etc. This isn't always the case. In descending acquisitions, the -1th slice is acquired first, the -2th slice tss later etc and in centric acquisitions the slice order is [2, 3, 1, 4, 0, 5] for a five slice acquisition. ukat should support these options and, ideally, custom acquisition orders.