Split app name and version in Capabilities.

To enhance capability matching and to select the latest version of the app to test if the
app version is not provided by the users. This enhancement still retains the backward 
compatibility when users specified an AUT as "appName:appVersion".

Signed-off-by: Binh Vu <bvu@paypal.com>
1. Add code to return null if "appName:appVersion" is not in the apps store.
2. Or to return "appName:appVersion" if it is found in apps store.