[Android] Embedded API Sample code

This is the initial version of Embedded API Sample code.
Which covers below API usage:
1. UI inflation
2. Dynamically create XWalkView
3. loadAppFromManifest
4. UI & Resource client
5. XWalkPreferences
6. Navigation
7. Pause & resume JS Timers
8. onHide() & onShow()

BUG=XWALK-1230