Change prefab replace option to ReplaceNameBased

[rfadeev]

This ensures prefab reference as serialize field in another object persists on corresponding .scml file reimport.

For example, imaging having behaviour like this

using UnityEngine;
using SpriterDotNetUnity;

public class SDNBehTest : MonoBehaviour
{
    [SerializeField]
    private SpriterDotNetBehaviour sdnPrefab;
}

And prefab generated by SpriterDotNet linked to sdnPrefab field in the scene. Reimporting .scml file will result in PrefabUtility.ReplacePrefab called with ReplacePrefabOptions.Default which results into prefab reference being lost for SDNBehTest in the scene.

Another thing. Even if prefab references is not the case for the project (for example prefabs are loaded via Resources by path), reimporting with ReplacePrefabOptions.Default results in internal prefab structure being changed dramatically on .scml file reimport (and source control diff would report that). This is undesired behavior for the case of .scml file was not changed.

Closes #73.