Add Polish Colemak-DH ANSI variant

This adds Polish ANSI variant for Colemak DH.

US version it is based upon, has different naming convention colemak_dh for ANSI version, and colemak_dh_iso for ISO one, but already defined Polish ISO variant is named colemak_dh, so I had to use colemak_dh_ansi for new one. I suppose it would be problematic, if I followed US naming convention, as there might be already users of existing variant…