Have window.create() call window.show().

E.g. if a notification is fired the app will be in the background, but then
that notification calls window.create(), we want the activity to show.
chrome.alarms: Make it more robust and prevent onLaunched when onAlarm is the cause of the Activity starting up

More robust by:
- Eliminated race condition with alarms firing during start-up
- Don't use evaluateJavaScript()
- Remove alarm entry before calling callback (exceptions caused alarms to re-fire)
Added getAccounts on Android.

Also updated the README, noting a divergence from the official spec.
Simplify chrome.alarms's java code
Refactor notifications to follow same paradigm as Alarms on Android

* Use a CallbackContext for native->JS
* Prevent onLaunched from being fired due to notfication events
Merge branch 'master' into android-service

Conflicts:
	chrome-cordova/plugins/chrome.notifications/src/android/ChromeNotifications.java
Remove debug log (whoops)
Merge branch 'master' into android-service
Add initial background-app plugin
Change default package id from com.your.company -> com.yourcompany
Make notifications, alarms, and window.show() use background-app plugin.

Also adds post-prepare logic to make MainActivity extend BackgroundAppMainActivity