Revert "Refactor Msg class"

[stefanu21]

This reverts commit c0f9d53.

This is a break in the api. Projects like icemon no longer works.

[ossilator]

this feels very wrong to me.
instead, the internal api should be properly versioned, and icemon (the only external consumer?) should have the required #ifdefs.

[stefanu21]

yes you are right but the mistake has already happened that the api is not versioned correctly. nevertheless there is no compelling reason to change the api like this and make the clients unusable. after all, this is just cosmetics. if it would be about projects that would be developed much further ok but neither icecc nor icemon has done anything substantial in the last years except the new scheduler modis...