Add experimental ds4vita plugin

[d-rez]

I don't think it's been released or anything but might be worth integrating. Current plugin is causing some unexpected behaviour in some games (related to deadzones and random right-stick behaviour in some games)

The experimental version was released by @xerpi for testing on reddit: https://www.reddit.com/r/vitahacks/comments/90z2ey/testers_needed_experimental_ds4vita_version/

The github branch is hooks, https://github.com/xerpi/ds4vita/tree/hooks

On the other hand, based on some feedbacks I've seen, the experimental plugin is causing some Adrenaline crashes (worth noting)

Thanks as always :)