Exclude build artifacts and Android Studio bits from final package

[vladimir-kotikov]

As suggested in #519, adding android build files and some additional files to .npmignore - this decreases size of final package to ~233 Kb (was ~26 Mb)

[msftclas]

Hi @vladimir-kotikov, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

It looks like you're a Microsoft contributor (Vladimir Kotikov). If you're full-time, we DON'T require a Contribution License Agreement. If you are a vendor, please DO sign the electronic Contribution License Agreement. It will take 2 minutes and there's no faxing! https://cla.microsoft.com.

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[richardhuaaa]

Great stuff @vladimir-kotikov!