Remove crosswalk internal dependency after Crosswalk Embedding API v2

Including following changes:
1. Use crosswalk's default implementatin for
   getVideoLoadingProgressView,
   onReceivedHttpAuthRequest,
   onReceivedSslError.
2. Move onPageStarted/Finshed to CordovaChromeClient
3. Remove the customView related code in CordovaWebView as it's
   dead code.
4. Override dispatchKeyEvent instead of onKeyUp of CordovaWebView
   due to the key event handling change in crosswalk.
Remove XWalkSettings dependency in CordovaWebView

XWalkSettings is not a public class in XWalk Embedding API.
Use XWalkPreferences instead.
Merge pull request #122 from wang16/embedding_v2

Remove crosswalk internal dependency after Crosswalk Embedding API v2