Improve error handling of project bundle in Designer

At this moment, the bundle parsing breaks when there is an error in the nuxeo-<project>-bundle.html file.
Although Designer does not rewrite the file because of these errors, we need to implement a better approach to parse the correct contributions and discard/solve the issues with the problematic ones.

A first implementation could try to parse one contribution at a time, catching exceptions and not breaking the process, but instead return the correctly parsed contributions and a list of the problems within the rest of the bundle.