Add a Frame Rate Setting

[CryZe]

We are currently throttling the framerate to 30 FPS. We could go up to the display's refresh rate, but that will negatively impact the battery usage. We probably want to introduce two different rendering modes:

• High Frame Rate
• Battery Friendly

You should be able to choose between them in the settings. Additionally we may want to have an automatic mode that uses the unfortunately deprecated Battery API to check if the device is plugged in and fully charged (?) to dynamically switch to High Frame Rate.

The exact details can be discussed in this issue or a PR.

[CryZe]

This can just be a toggle down here. I don't think we want to use the battery API: