EllipComp and walker initialization

[marusazerjal]

Tim: To ensure the emcee parameters are always initialised in a valid way when calling compfitter.get_init_emcee_pos I hacked in a little loop that goes through each initial walker’s position, and forces dx>dy and du>dv. It’s not super tidy. Much nicer would be a way to edit EllipComponent.SENSIBLE_WALKER_SPREAD such that, if an init component already has dx > dy and du > dv, then getting a swarm of walkers centred on this init_comp’s emcee_pars should rarely yield an invalid component. But I don’t know enough about how Neelesh’s ellipcomponent is implemented to recommend how to do this (or even if it would work).