Add preference to move alt-tab panel up/down display

[mogthew]

Is your feature suggestion related to a problem? Please describe.
On large screens, the alt-tab panel displaying at 1/3 down the screen requires me to move my head/eyes from where I'm normally looking.

Describe the solution you'd like
Add an option to center or add y-offset to display position

Describe alternatives you've considered
Exact screen center (probably requires more work)
User specified y-offset (likely easier?)

[lwouis]

Duplicate of #585