Fix behaviour of two-arg key properties

As things really need to be done 'by hand', it makes
more sense to use \exp_args:... directly for many of the cases.
At the same time, a bit of rationalisation of variants: this should
be enough for the 'common cases'.


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4520 de43f980-851b-0410-b2f7-c40aca1f87e0
First sweep making label/ref markers module-specific

Probably there are a few to check again!


git-svn-id: http://www.latex-project.org/svnroot/experimental/trunk@4521 de43f980-851b-0410-b2f7-c40aca1f87e0