pageSetup.py: local_css() doesn't handle file not found condition

[billschereriii]

Description

In pageSetup.py, local_css() doesn't handle a file not found condition, which will mean sending an exception back to the caller. Even if it's a internal configuration error, we should handle this gracefully.

Justification

If the dashboard just crashes out, users will have a frustrating experience. If it reports an error, they can at least use other parts and can tell us better what's wrong.

Implementation Strategy

Add an except block