Add license management frontend

What does this MR do?

It adds approval and blacklist frontend for software licenses; see https://gitlab.com/gitlab-org/gitlab-ee/issues/5488

Why was this MR needed?

To implement https://gitlab.com/gitlab-org/gitlab-ee/issues/5488

Screenshots

Screenshot	Description
behavior-mr-widget	MR Widget behaviour (still with the old widget style)
	MR Widget
	MR Widget Approval Modal of unapproved
	MR Widget Approval Modal of approved
	MR Widget Approval Modal of blacklisted
license-management-behaviour	LM behaviour
	LM empty
	LM
	LM delete confirmation

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conforms to the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5488 (closed)