Fix Android sample app

[AbigailMcP]

Includes a couple of fixes to the Android sample app:

• Adding a .png icon file
• Adding expected index.android.js entry point

[mcdaniel67]

I was planning to pull locally and test, but ccoenraets's repo doesn't have good Android documentation. Only really had one point which could be taken as OOS. We could also consider adding instructions for Android in the Cavy example docs.

[mcdaniel67]

It's possible to knock out #55 at the same time. Not sure if it's totally out of scope for this change.

[jalada]

@mcdaniel67 you're right, the documentation is thin on the ground and a bit outdated. I'll add another note to pull in our own documentation. For now, you should be able to follow the standard process for setting up an app; the code is just JS.