Minor tweaks

Milestone markers now go at the very front, as well as the today line.
Better error checking inside the script.
Switched the order of the ID and swimline columns in bar dna mislestone
tab
Added a convenience formula so that the milestone swimline is read from
the parentbar, but note that is totally optional, the script doesnt know
about that parent bar, just checks the swimline column to position the
milestone marker.
Tweaked the colour labels to show options also fixed the colorize
function to accept direct rgb values to avoid relying on the labels when
used internally.