box problems: do not call the name() method before the init() method was called

this allows to first construct the problem, then set a name and then
run it which allows to avoid quite a few ugly hacks...

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@5373 2fb0f335-1f38-0410-981e-8018bf24f1b0