Shake detector is working when the application is in background

[pedrovgs]

Steps to reproduce:

1. Initialize LynxShakeDetector inside Application onCreate method.
2. Close the application without kill it. You can pulse the home button.
3. Shake your phone.

Bug: LynxActivity is opened even when the app is in background.

Fix: This behaviour should be configurable in LynxShakeDetector. Add code and tests to fix this issue.

[pedrovgs]

@flipper83 you reported this bug, can you fix it?

[flipper83]

me?? "pedrovgs opened this issue 2 minutes ago" but I can help you to close it jaajajaj

[pedrovgs]

You reported the bug, you can fix it ;) No more than 1 hour of your time. I promise!

[vic-gonzi]

I'll take this one ;) .

There is another reason to fix this issue. Shake detector gets disabled when LynxActivity is launched, to avoid launching more instances, but when shaking on background shake detector is not stopped. Thus, when reproducing this error you'll also need to press back button several times to return to main activity.

[pedrovgs]

Thanks @vic-gonzi waiting for your PR :)