Iterables Feature Request - Expanded

[dirtyonekanobi]

This pr expounds on terlmen0's PR #218 (with permission) - but makes the following changes:

• Instead of implementing a separate model for Iterables/Itervalues, we take an approach similar to the way Networks handle adjacencies.
• Parent/children of iterables are in the same model
• introduced a 'value' to the Iterables model
• Iterables are now a Resource and can be queried using attributes
• adjusted the get_next_value() iterable method to account for children

Please feel free to suggest any changes. Thank you!

[jathanism]

@dirtyonekanobi Just taking a look at this now. Thank you so much for contributing.

[jathanism]

Hey let's keep this moving! Let's get this updated for the latest release and get the tests working.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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