Handle user pressing cancel button, on Android

[shiv19]

If this PR is merged,
When user cancels image capture, the promise is rejected with a message "cancelled"
{onAndroid}

[andreacappadona17]

Hi, I tried adding those lines to the plugin, to check if everything was right, but on my Samsung J5 2017 the app still crashed.

Debugging, I found out the callback for "activityResult" was called twice, when you take a picture after pressing cancel button the first time.

Managed to make the app work by adding

appModule_1.android.off("activityResult");

before

appModule_1.android.on("activityResult"...

[shiv19]

@andreacappadona17 Thanks for pointing it out.
I've incorporated the changes. Now the PR can be merged :)

[DimitarTachev]

Great work, @shiv19 and @andreacappadona17. Could you just fix the linting error from the Travis report in order to merge the PR. ('ERROR: camera.android.ts[87, 1]: trailing whitespace')

[jlooper]

Congratulations on this quality PR! Have a badge!

[DimitarTachev]

@shiv19 @andreacappadona17 I cherry-picked the changes and rebased them as we already merged PR #66 and there were some conflicts. The changes will be merges with PR #67

[DimitarTachev]

The changes were merged with PR #67

[shiv19]

@DimitarTachev and @jlooper Thank you! 😄