Import 1086791f3e: Refresh rate now Target FPS; decoupled it from presets (by Caitlyn)

This is an automated proposal to look at a commit made by Caitlyn and import it into Overte

Commit:	1086791f3efebb571e1ee2abb2d7f2da1c328581
Author:	Caitlyn
Date:	Mon, 06 Apr 2020 14:29

Refresh rate now Target FPS; decoupled it from presets

Stats:

Filename	Stats	Lines	Added	Removed	Lines in blame
interface/resources/qml/hifi/dialogs/graphics/GraphicsSettings.qml		8	4	4	⚠ File gone
interface/src/PerformanceManager.cpp		4	2	2	⚠ 0
2 files	-	12	6	6	0

To work on this, please assign the issue to yourself, then look at the commit and decide whether this would be a good addition to Overte.

If the commit is useful, tag it with "Tivoli: Keep", and keep it open until it's merged.
If the commit is not useful, tag it with "Tivoli: Discard", and close it.
If the commit is not useful right now, but might be later, tag it with "Tivoli: Maybe later", and close it.
If it's hard to decide, tag it with "Tivoli: Discuss", and keep it open.

Useful commits should be submitted as a PR against Overte. Tag this issue in PR, so that it's automatically closed once the PR is merged.

You can cherry-pick this issue with this command:

git cherry-pick 1086791f3efebb571e1ee2abb2d7f2da1c328581

overte-org / tivolicloud