Improvements to exception handling to avoid hiding unexpected errors

[elichad]

I spotted that #192 and #196 both report problems that are hidden/obfuscated by the except Exception: pattern used in a lot of the Python checks for catching and logging errors.

I suggest that exception handling could be improved throughout:

• narrower catching of specific exception types that are expected to be triggered in certain circumstances (like FileNotFoundError in False "not UTF-8 encoded" issue in metadata-only validation against the ro-crate-1.2 profile #192)
• prevent checks which throw unexpected exceptions from being silently skipped - they should fail, or at least a visible warning should be printed (not just a debug log which most people never see)