[Android] Support using intent to launch url in core shell

It's inefficient for developers to type complex urls in core
shell for debugging and testing.
Add a broadcast receiver in core shell activity to receive
intent to launch url.
Developers can use adb to send the intent like:
adb shell am broadcast -a org.xwalk.core.xwview.shell.launch -e url <url>
Merge pull request #1483 from wang16/intent_launch_url

[Android] Support using intent to launch url in core shell