Implement categorical and primary metadata search

[rtibbles]

Objective: Kolibri and Kolibri Studio users are able to use categories and other metadata filters to quickly hone in on resources that are most relevant to their needs

• Kolibri Studio users can efficiently update tags and metadata for new and existing resources
• The Kolibri ecosystem supports new metadata:
  • Estimated time for resource completion
  • User facing learning activity categorization
  • Hierarchical tagsonomies like 'Subject'
• Browse and search for resources in Kolibri and Kolibri Studio using categories and metadata as primary filtering mechanisms

[jtamiace]

Specs for the learning platform: https://www.figma.com/file/uiZuCIqh2KYvBUfbCiJyyA/Hybrid-Learning?node-id=9%3A2