DataSync tizen plugin implementation

SPEC=https://developer.tizen.org/dev-guide/2.2.1/org.tizen.web.device.apireference/tizen/datasync.html

BUG=XWALK-1061

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Running TCT:
 - install rpms on device:
     - libwbxml2,
     - sync-agent,
     - oma-ds-agent (and start: systemctl start oma-ds-agent.service),
 - copy 'tct-datasync-tizen-tests.wgt' to device,
 - install and run application,

Current TCT datasync passrate: 63/63

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As it mainly carries data, what about define it as `struct`, so you can get rid of all these tons of getter/setters.
ref  [Structs vs. Classes](http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Structs_vs._Classes)