Add mobile 'source' getPageSourceXML

Example Ruby use:

mobile :source, type: :json
mobile :source, type: :xml

Fix #349
Merge pull request #350 from bootstraponline/source_xml

Add mobile 'source' getPageSourceXML
don't set type of real device, and add instruments launch logging
enable setting device orientation in desired caps
allow overloading of this selenium desired cap
add --orientation cli param
Updated Java Appium examples and documentation