Add support for open intervals

[tillschallau]

Description of bug
It is not easy to add an open interval to temporal operators.

Steps to reproduce

$\phi \cuntil[[0,\infty)] \psi$

This gives the following error: Extra }, or forgotten \endgroup.

Temporary solution
Create a new group around the opening [:

$\phi \cuntil[{[}0,\infty)] \psi$