to use transform module instead of image.voxToWorld/worldToVox methods

displayCtx.bounds, rather than imageList.bounds. This also means that
the SliceCanvas needs to be given a display context.

coordinate systemss, with the ultimate aim of having the location panel
always reporting image world coordinates, regardless of the way in which
images are being displayed.

import issues

view panel was opened/closed.

destroy. Orthopanel was showing/hiding wrong canvases in grid
layout. Canvas panel was using wrong sizer flags for colour
bar/canvases.

'refreshLabels'. Added little hack to support orthographic display -
invert horizontal axis on X canvas when in grid layout.

relative to each other. Also explicitly setting  label background colours.

come. Also fixed SpacePanel to bring it in line with anatomical label
scheme.

subclasses can just use self._name when registering on the same
properties

defined (and correct!).

than an actual feature.

do not have config options, but also do not have a config menu item
name. 2. Conflicting fslview cli args - -a[lpha] and -a[xis]. Latter
changed to -ax.

axes. These are exposed to the user by Orthopanel for the time being,
but will be removed at some stage.

reset whenever the image bounds or Z axis is changed.

change when the image properties change).

on image bounds change. I'm going to change lb canvas a bit, as I don't
like its behaviour.

lightbox canvas - only draw cursor/gridlines if there are images being
displayed.

SliceCanvas, whic calculates pixel dimensions