Allow colourmap/lut files to be specified on command line
e.g.
fsleyes image.nii.gz -cm `path/to/my/custom/colourmap.cmap
A colour map specified in this way should not be installed permanently.
e.g.
fsleyes image.nii.gz -cm `path/to/my/custom/colourmap.cmap
A colour map specified in this way should not be installed permanently.