Make NPatchData receive LoadComplete call from TextureManager.

Make NPatchData receive LoadComplete call from TextureManager.

 - If an NPatchVisual is destroyed before it receives LoadComplete,
   the loading process of the npatch image is never completed.
 - At that time, because the cache data is already created, every request of the image after that is ignored.
 - In this patch, NPatchData is separated from NpatchLoader and NPatchData request npatch loading to Texture Manager instead of NPatchVisual as a representative.
 - After the loading is completed, NPatchData receives LoadComplete call and makes textureSet.
 - And, The NpatchData sends UploadComplete call to the each NPatchVisuals those originally request it.

 + Additionally, this patch includes an method to remove unused cached data.

Change-Id: I0879a9eaa62aac8533fbc6b8d9416805ab7a0675
Signed-off-by: Seungho Baek <sbsh.baek@samsung.com>