We used __subclasses__(), but this only returns the immediate
subclasses and not all further/nested subclasses. Instead, we must
use the pySim.utils.all_subclasses() function to really get all of them.
The hack to use the method signature of the constructor to determine if
it's an intermediate class didn't work, as even GlobbalPlatformISDR
has a optional argument for non-default AIDs. So let's introduce an
explicit class attribute for that purpose.
Change-Id: I7fb1637f8f7a149b536c4d77dac92736c526aa6c
dffe7af578