[Android] Embedding API v2 part 1

This commit added following APIs as Embedding API:
XWalkResourceClient.shouldOverrideURLLoading
XWalkUIClient.onUnhandledKeyEvent
XWalkUIClient.shouldOverrideKeyEvent
XWalkUIClient.onReceivedTitle

Those APIs were implemented inside xwalk core internal
before this change. Now moving them to public Client
classes of XWalkView to expose in Embedding API.

Beside, remove the internal callbacks which are decided
not to expose in Embedding API and currently are dead code
or have empty implementation in core internal, including:
XWalkWebChromeClient.onReceivedTouchIconUrl
XWalkWebChromeClient.getDefaultVideoPoster
XWalkWebChromeClient.getVideoLoadingProgressView

BUG=XWALK-2003, XWALK-2004