Setup initial Vue app for design management

What does this MR do?

Creates & setups the initial Vue app for design management.

It uses Vue Router so that we can easily manage the root view, which will show all designs, and the individual design view, which will show the design, details and discussions etc. At the moment it uses hash for the mode where it would be nicer to use history, however that requires some Ruby changes that I would prefer to avoid for now.

Sets up GraphQL with the ability to use apollo-link-state for local state management.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer