Create penalty changing system

[rpspringuel]

Basically something like what I did for the distances: create a system which provides the user with a convenient interface for changing the various penalties without having to redefine commands.

[henryso]

From @eroux (on gregorio-devel):

I think the penalties should just be mapped to some \gre@space@count@xxxpenalty counts (no need to make it macros, they can be count directly), that's it... about the deprecation, I really don't think it's necessary, I don't believe many gregorio users know what a penalty is... and those who know will certainly be the kind of persons to look at UPGRADE.md.

[henryso]

There are some numbers in gsp-default.tex like \grewidowpenalty and \grelooseness which are not passed to \gre@penalty but are set into things \widowpenalty = \grewidowpenalty and \looseness = \grelooseness. Should we handle these in the same way?

[eroux]

I think so yes. Also, keep in mind that the same kind of system (mapping to count) will be used for protrusion factors too