I'm afraid you can't disable all of them at once, just on an app-to-app basis, but it's a convoluted process.
first, you'll need to pull down the notification shade and tap and hold the settings icon (the small cogwheel one) until you feel a slight vibration. then, open settings and scroll down to the very bottom. you should have System UI Tuner entry there. open it and then head into Other > Power notification controls and toggle it on.
if you followed the above steps, you can now go to Settings > Apps and choose the app you want to disable peek notifications of. open the app's properties screen, go to Notifications, and tap the green A icon under "Importance". now you can edit the notification's importance. there are 5 levels from 0 to 4. importance of level 3 and below means there won't be peek notifications from this app.
once again, there's no way to do that for all apps at once.
