"True" Mirrored Mode

[justMaku]

This PR add support to "true" mirrored mode where the image on odd displays is flipped horizontally. The old "mirrored" mode has been renamed to "cloned".

Existing users will have to manually switch to the new mirroring behavior otherwise they will stay in the old mode.

Here's some previews:

[glouel]

Hi @justMaku !

Thanks a lot for the PR, this looks pretty cool ! I'm going to be pretty busy in the coming days so I may not be able to merge and release a new version until monday.

I saw you put the new mirrored at the end of the enum so that's great, it won't mess with current user's settings.

One thing come to mind, it looks like you're using the index in which the system has called us. Off the top of my head, we're called on main screen first then the other screens. But it's not position dependant. If you had an iMac with one screen on the right, and one on the left, you'd want main (0) normal, and 1 and 2 flipped too to keep the effect.

I'm not sure that's a big issue as the number of complex screen configuration users is pretty small, and they may not want a double flipping anyway in that case I mentionned (may look a bit jarring unlike a 2 way mirror effect which looks pretty cool I think).

I do have some code to detect screen's relative position but it's a big mess because you can have screens in 2 directions with overlap, so I'd avoid going in there. And in the same way, if vertical mirroring, I'm not sure flipping would be good, that would truly be jarring ;)

So I'd say let's add it as is, and if people with more complex configurations wants more, it can always be perfected a bit.

Thanks again!

[glouel]

Well, didn't hear back from you but merging as is.