Rename MintableMultiownedToken

MintableMultiownedToken is not only MintableMultiowned, it is more dividendsToken

[Eenae]

Maybe it's even better to split it as MintableEmissionCapableMultiownedToken as a descendant of MintableMultiownedToken (which is std, multiowned, mintable).

[Eenae]

@quark8 review please