I did mention that I upgraded to Lollipop.
I forgot to mention that a consequence of that upgrade is that Xposed Modules no longer work (and hence the knock knock module you posted doesn't work sadface). I have lost a lot of functionality that I would like back at some stage, but lollipop is good enough that I'm persisting with it and not going back to 4.4.4.
To do this in Lollipop requires 2 parts...
DT2W - Double Tap to Wake - Use a custom kernel like Hellscore... this requires Root, the kernel, a kernel manager to set options (Hellscore Kernel Manager), and setting SELinux security to Permissive, it works well and is pretty easy on battery, the battery you lose using the DT2W option is gained from the customer kernel, so it's about a wash compared to stock kernel.
DT2S - Double Tap to Sleep - Use Nova Launcher... set a shortcut for gesture Double Tap to a an app that puts the phone to sleep, take your pick, there are lots in the Play Store.
Its not difficult, no power button needed, no Xposed, so tricky apps or any anything terrible that can't be quickly undone.