Refactoring npatch-loader so it works well both sync-async loading

Make async loading always call LoadComplete when we try to load n-patch image.
+
Releative with both sync-async case,
Fix minor reference count issue for NPatchData.
Previous logic only control refrence count as Observer. It was not good.
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Fix minor caching issue with border.
Previous code logic have problem when we use same Url and different border.

Change-Id: Ic54dd522e44f5db64f3e9d08aa44db224ab4d506
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>