Be more robust to issues with the flowsheets

[dangunter]

Fixes #54 , #57

Changes

For Issue #54:

• Check if attribute exists, if so proceed
• If not, set the label to "None"
• Could issue a warning, but that would probably be ignored in this context and anyways there will be warnings issued from the idaes core code that builds the stream table earlier in the processing.

For Issue #57:

• Add 'strict' mode to validation, off by default
• Change failure for missing components in layout to warning in default (non-strict) mode

For general amusement:

• added some debug statements into the web server

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the license terms described in the LICENSE.txt file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.