Firebase functions init

[pavel-ilin]

Fixes for issue: #9

Before work with functions and deploy them please read firebase docs and install all necessary dependencies.

Functions are are working independently from React Native. Functions can be used to update firestore.

in root directory you can find functions directory which contain all necessary dependencies and functions.

For now it have only index.js with hello world function. We can add more functions there.

I think with that we can close issue #9 and create new issues for specific functions we want to deploy.

p.s. removed react-native-firebas from the package.json