Saving and loading locations

[xuelongmu]

Summary

WIP technical implementation for #9. Saving / loading locations to disk are working.

Debug controls (should be removed before merge, in BP_SavedLocationComponent):

• 9 to save current location
• 0 to print current list of saved locations to screen

Author checklist

• Tutorial for #9
• Has the new tutorial been integrated into the main level? No
• Has a new section of the readme been added for this tutorial? No
• Have you done a full self-review of the code and blueprints? No
• Have you tagged a primary reviewer? Yes
• Are there any remaining tasks to do or blocking questions to answer before we can merge this? Yes
• [x] Implement UI

Testing plan

Reminders for reviewers

Thank you for taking the time to review this PR. By approving a PR you are taking as much responsibility for these changes as the author. Please keep these points in mind throughout the review process:

• Review and run all parts of the test plan on this branch and verify it matches expectations.
• Review the code and make sure you do not have any remaining questions or concerns. You should understand why this code change fixes the issue and agree that it's the best approach to doing so.
• Review the automated tests and make sure there are no missing tests or edge cases.
• When you feel this is ready bump it to a second reviewer or merge.

[CesiumBen]

@xuelongmu UI for saved locations have been added in. The portions you pushed look great, and worked as expected for the UI.

[CesiumBen]

@xuelongmu I pushed an update to to the tutorial to close the menu when you move away from it. Ready for re-review.

[xuelongmu]

Looks good! We'll want to update the tutorial with the close menu functionality.