instead of turning it off by defining DUNE_XT_FUNCTIONS_DISABLE_CHECKS
you can now enable it by defining DUNE_XT_FUNCTIONS_ENABLE_CHECKS

also add adjustable compare tolerance

[expression.timedependent] remove

This is not actually necessary. Adding a handler for std::exception also
hid the more specialized handlers provided by pybind11 itself.

[test.affine] actually test something

to be both available in bindings, and not cause a stackoverflow in
copying tmp values

[lambda.global-flux-function] fix segfault

Actually add exceptions that were deprecated in dune-xt-common

Add is_affine() method to LocalizableFluxFunctionInterface