fix typesetting for newer sage versions

Since version 4.12 sage doesn't support the command sage.misc.latex.pretty_print_default anymore.
Instead we use the %display ipython magic. In order to keep the code clean the
specific commands have moved to a dedicated python function "__cantor_enable_typesetting(enable)"
that gets declared on init and called by the backend when needed.
This patch also introduces a finer handling of version numbers instead of just having a simple
"legacy mode".

Tested with Sage versions 5.10 (old commands) and 5.12 (new command)


FIXED-IN: 4.12
(cherry picked from commit c3626842a34bd324d271a54b05076840cbd6e616)