make ignoring of polytomies default for ASTRAL-PRO

Since ASTRAL-PRO is known not to work great when allowing for polytomies (which happens quite often with fasttree output), I propose to - by default - disallow for polytomies. I therefore created a new commandline argument --allow-polytomies for pantools consensus_tree, by which users can select the original default. Do you think this is a useful addition? Or should we disallow for polytomies altogether (thus enabling us to update the submodule of ASTER to the latest version)?