ttools: add a new colour map Rainbow2.

This shader is copied from the glNemo2 application by scraping the
pixels from a screenshot.  A new class LutSteal is added to facilitate
this.
topcat: sky plot position formatting now honours sex/dec setting.
ttools: keep order of task parameters.

Use a LinkedHashMap rather than HashMap to keep parameter name/value
pairs so that the order is preserved.  This doesn't really change
behaviour, but can lead to better-organised error messages etc.
ttools: fix cube aspect config bug

Logic was wrong for isotropic/anisotropic selection of aspect config variables.
ttools: add a couple more colour maps.

Added Accent and Cold.  These were scavenged from the WWW and converted
to .lut files using ttools.plot.LutSteal.
ttools: remove range limitation on Subrange values.

Previously the (lo,hi) values of a subrange were constrained to be in
the range 0..1.  There is no particular reason for this limitation,
so it's been removed.  I thought I wanted to do something with longer
ranges, but at present I don't think I do, so this extended functionality
is not currently used or tested.
ttools: allow colour map range restriction.

Aux and density colour maps now come with a clip config control
which allows you to select which region of the colour map to use
(by default you get it all).  In conjunction with the fairly extensive
colour map library supplied, this gives you quite a lot of control
over what colour maps you use.