Crashfix: Forbid unloading of python mod

[michaelortmann]

Found by: Patch by: michaelortmann Fixes: #1626

One-line summary: Forbid unloading of python mod

Additional description (if needed): Currently there is no way to avoid / fix crashes and other obstacles with unload/reload of embedded python

Test cases demonstrating functionality (if applicable):

.load python
[17:01:54] tcl: builtin dcc call: *dcc:loadmod -HQ 1 python
[17:01:54] Module loaded: python          
[17:01:54] #-HQ# loadmod python
Module loaded: python          
.unload python
[17:01:56] tcl: builtin dcc call: *dcc:unloadmod -HQ 1 python
Error unloading module: python: The python module is not allowed to be unloaded.