Fix for rbx
Fix for rbx

It's not that crucial to treat relation as an abstract class and since
it breaks rbx it's better to leave it like that.

If somebody, for whatever reason, instantiates Relation class it would
still work wrt dataset handling

rom-rb/rom,rom-rb/rom,endash/rom,pxlpnk/rom,jeremyf/rom,cored/rom,denyago/rom,kwando/rom,dcarral/rom,pdswan/rom,pvcarrera/rom,vrish88/rom,dekz/rom,Snuff/rom,rom-rb/rom