Change play.api.data.Mapping properties to defs
Change play.api.data.Mapping properties to defs

Making them vals can cause initialisation issues, and isn't necessary
here.

marcospereira/playframework,wegtam/playframework,benmccann/playframework,mkurz/playframework,benmccann/playframework,mkurz/playframework,playframework/playframework,playframework/playframework,marcospereira/playframework,benmccann/playframework,mkurz/playframework,marcospereira/playframework,playframework/playframework,benmccann/playframework,mkurz/playframework,wegtam/playframework,wegtam/playframework,wegtam/playframework,marcospereira/playframework