Set CSS top for the placeholder contentContainer

# Problem
The content container would disappear off the viewport if the top was not set
# Solution
Set CSS top for the placeholder contentContainer
# How to test
- Checkout this branch
- `./init.sh && grunt qa` tests should pass
- your browser should open localhost:9000
- click the scrollList demo
- inspect the DOM and find the element with class `scrollList-contentContainer`
- That element should have a top and left 0px CSS property
![image](https://cloud.githubusercontent.com/assets/6053699/3807299/84506380-1c63-11e4-9d70-b570b9b7982d.png)

# Unit test
- updated to check for 0px

@timmccall-wf @patkujawa-wf @georgelesica-wf @tomconnell-wf @todbachman-wf 
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