Backendlib should provide installed_time, installed_size, app_size, data_size

BUG=XWALK-2459

backendlib should set those field in pkgmgr detail info structure.

pkgcmd -s -t wgt -q -n ${pkgId} # should return this data

This information may be present in other apps to user if he/she want to install app.
sorry, maybe I should have mentioned it before but now I see that: 'CountAppTotalSize', 'CountAppDataSize' and 'GetApplicationInstallationTime' are aux functions only used in ' application/tools/tizen/xwalk_backend_plugin.cc ' so think it's better to move them there to an anonymous namespace  (unless you think there will be other clients for these function in the nearest future).

LGTM otherwise