[Tizen] Generate Camera from loaded model

[Tizen] Generate Camera from loaded model

This is a combination of 2 commits.

Refactoring model-impl.cpp

 - Extract some method to reduce duplicated code.
 - Reduce braces depth
 - Use return early for easy understanding
 - Separate too long method

Generate Camera from loaded model

Add API to generete (or apply) the camera what 3D model has.

Note that model cannot have ownership of camera
since we have to add camera into SceneView or whatever we want.
So GenerateCamera create new CameraActor everytime.
Or ApplyCamera into already created CameraActor.

TODO : Should we change all Scene3D::Loader used demo who use camera parameter?

Change-Id: I3900090fc52487c03ce9c66bfc79b31ae8b9e27e
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>