UnknownModuleError exception is missing

[snegovick]

Describe the bug UnknownModuleError is thrown but is not declared anywhere

To Reproduce Write some code with missing module

Expected behavior Implement exception in scl.py

Screenshots N/A

Environment (please complete the following information):

• OS: Linux
• Version https://github.com/snegovick/bcad/commit/dc6130336314a638a8339fd73e505cb298da19a8

Additional context None