Adding possibility to send userproperties to UIAutomator

Example:
<uiautomator>
	<propertiesKeyPrefix>Prefix</propertiesKeyPrefix>
</uiautomator>

> mvn <goal> -DPrefixKey=Value
Documenting the <propertiesKeyPrefix> more thoroughly.
Merge pull request #211 from SimonTurfer/master

Adding possibility to send userProperties to UIAutomator