Nsot

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* Enabled caching for Interface API endpoints.
* Cache is invalidated on save or delete of an Interface object.

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* Removed stale deps. and updated core deps. to latest stable versions

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* Bugfix when explicitly setting ``parent_id=None`` on Interface create.

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* Implemented bulk update of all objects using the REST API.
* Objects can now be bulk-updated using PUT by providing a list of
updated objects as the payload.
* Unit tests have been updated accordingly to test for both bulk create
and bulk update.

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* Added a Vagrantfile, improved documentation, and made some UX fixes.
* Read auth header from settings vs. hard-coded inside of user_proxy
command (fix 57)
* User proxy now also defers to default values from within settings.py
* Added a vagrant directory containing a Vagrantfile to bootstrap NSoT
in a self-contained virtual machine
* Added a new 'assignments' endpoint for Networks, to tell where they
are being
assigned to Interfaces.
* Added new nsot.utils.stats and ability to calculate network
utilization.

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* Always return empty query when set query is invalid (fix 99)