Remove requirement that Axes[0] == X && Axes[1] == Y

There are a number of places in IJ2 where an algorithm assumes the x coordinate of a position array is at index 0 and the y coordinate of a position array is at index 1. Remove this assumption.

Might need to have a Dataset cache the xIndex & yIndex (or more appropriately uIndex & vIndex) and allow them to be queried. One could supply methods somewhere such as:
fillPosition(uAxisIndex, vAxisIndex, uVal , vVal, planePosVals)
getU(position)
getV(position)
getPlanePos(position)

Migrated-From: http://trac.imagej.net/ticket/432

Start by locating the IJ2 code paths that assume x and y are at positions 0 and 1, then inspect the Dataset and position-array handling mentioned in the issue. Done means coordinate access works when the u/v or x/y axes occur at different indices, with the relevant callers updated consistently.

Written by the indexing model from the issue text.