Improve logging by catching exceptions and printing helpful custom messages

[amimas]

This issue is created from the following discussion thread in a PR:

#582 (comment)

Currently, exceptions are not being caught. GitLabForm will exit or continue based on whether --terminate flag is set or not. If it is set, the CLI will exit right away. Otherwise (default) it will print the exception and continue with rest of the process.

It might be good to catch the exceptions and then log custom messages about what happened or hints about how to fix it. For debugging purpose, the exception trace should be printed/logged as well.