[Tizen/Desktop] Prepare app installation code for using from xwalkctl

SSIA. Application storage and installer were moved to the 'common' folder,
'xwalk_application_common.gypi' was created to be further used by xwalkctl.
Besides, this patch removes the unused "db_store" code.
Merge pull request #2125 from pozdnyakov/app_installation

[Tizen/Desktop] Prepare app installation code for using from xwalkctl