User Interface for 3.x

[EricWittmann]

This pull request includes the following changes to the UI to reflect 3.x concepts:

• Option to search for (explore) Groups or Artifacts (with versions coming later)
• Ability to create an empty artifact
• Enhanced filtering UI
• Abilty to create a Group
• Group management (manage metadata, delete a group, etc)
• Updated Artifact details page, allows browsing versions
• Ability to manage artifact metadata
• New Group details page, allows listing artifacts in group and managing metadata

[apicurio-bot[bot]]

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