Convert ola_e131 to our flags module and do some associated work around that

Will do, makes sense to match the other bits, althoguh I perhaps need to document better how it's only used by the bool option.

Actually, how do you feel about breaking the internal code functionality, if I swap it so everything defaults to needing an option (so the default bool behaviour is "--foo true"), then the exception is the option less bool of --foo, with a has_arg of false?