Expanding Computer Vision for image classification

[ryanwelcher]

Description of the Change

This PR is intended to address the items requested in #75.

Items to be addressed:

• hook to catch the alt text being sent back from the Azure API (in case these need to be presented/filtered by specific consumer integrations)
• Automated tagging
• All automated tasks available to turn on/off via Settings
• UI for filtering in the Media Library (currently in backbone.js) and then batch sending images for alt text classifying
• UI to add tags alongside automated ones
• ability to remove automated tags
• error messaging or hook available to catch when ClassifAI doesn't match something for an image's alt text

** New items Aug/20/2019**

• Refactor to a single endpoint
• Add taxonomy selector for Image Tagging
• Remove custom taxonomies from Media Library modal UI

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.