Fix some listings/minted incompatibilities

Fix some listings/minted incompatibilities

The basic problem here is that rather than using an abstract syntax,
backend-specific param strings are produced in the listings dialog,
depending on whether listings or minted is used.

Of course this breaks if a user switches backends inbetween (s/he would
have to open and re-apply each and every listings inset!)

Do at least the most basic translations in InsetListings::latex().
A sane solution would imply the use of only one param syntax with
respective interpretation for each backend. But this would be a file
format change.