latexsupport: minor changes for tex4ht

- added in a description environment that is formatted as atable
(sldes2)
- some additions to css
- fixed formatting of sstattributes (used in kappa sun95)
kappa sun95: minor changes to work with tex4ht

- fixed \att to be a regular latex style command.
- changed 'verse' to 'description' where appropriate in
graphical styling
- tested new description like environment (sldes2)
which is formatted as  a table in tex4ht.
latexsupport: fix typo in some starstyle.sty command definitions
latexsupport: starstyle.4ht now ignores optional args to descripiton

Previously if optional argument was given to a description
environment tex4ht would issue an error about extra braces at the
first item [TITLE] command. Quick hack found on stackoverflow
to force it to ignore the optional arguments has been added.
kappa: updated a few lists to be more sensible in sun95.tex
Docs: sc21.tex: fixed some heading formatting
kappa: sun95. removed unecessary appendix renumbering.
latexsupport: fixed sstattribute definition in sst.4ht
kappa sun95: replaced \rm with \textrm
latexsupport; css on images improved
latexsupport: improved tex4ht sectioning
latexsupport: require siunitx in starlink.cls
kappa: sun95.tex: hacky temporary fix for degrees symbol

uses an \ifpdf option in preamble. Should be moved into packages
kappa: sun95.tex: altered \tt to be \texttt commands
docs: sc21.tex: fixed stretching of figure sc21_curveofgrowth
latexsupport: tidying up of .4ht, .cfg and .sty files
latexsupport: fixed crosslinks so they dont hide footnotes