Add the ability to define the positive direction of an axis to LiveGrid.
Add the ability to define the positive direction of an axis to LiveGrid.

In order to resolve an issue at SRX, whereby they purposely want to
invert (make the positive direction being down) the y axis in LiveGrid
due to their scanning process producing an inverted image in this
direction. As this is likely to be a problem whenever scanning
'imaging' modes are used, and the sample is moved instead of the beam,

ericdill/bluesky,ericdill/bluesky