Toolbar needs touch slop (press becomes drag too easily)

[Toby Kurien]

Problem:
Hard to click on toolbar (swipe-up-from-bottom menu) items, especially if using the side of your finger.

Detail:
Like Android's touch slop (https://developer.android.com/reference/android/view/ViewConfiguration.html#getScaledTouchSlop%28%29), the Ubuntu toolbar needs a touch slop. Currently, if you press a toolbar item with the side of your finger, it appears to Ubuntu as a very small distance drag, and so the item click is ignored. A click thus requires a very steady and assertive press.

How to reproduce:
- Open Calendar app
- Swipe up to reveal toolbar
- Press any item with the side of your finger, or move your finger slightly as it touches the screen
- Often the click is ignored and the toolbar slides slightly, indicating a drag event

Expected result:
- Only a drag of more than <touch slop> grid units should result in a drag event. For smaller drags, it should be considered a click.

Tested on:
HARDWARE=grouper
JENKINS_BUILD=saucy-35
UBUNTU=ubuntu-touch-saucy-armhf
ubuntu/platform-api=:84
hybris=0.1.0+git20130606+c5d897a-0ubuntu9
apt updated today (11/07/2013)