Extract firebase helpers initialization

[martynovs]

Description

Extract initialization to separate module will allow to configure more than one firebase app and use externally loaded firebase (from firebase hosting, not from npm).
Also library will not dictate to use it's compose, in my case I use compose from redux dev tools.

store configuration may look like this:

import firebaseInit from 'react-redux-firebase/src/init';

function attachFirebaseToStore(store, config, name) {
  const app = firebase.initializeApp(config, name);
  const instance = firebaseInit(app, config, store.dispatch);
  store.firebase = instance;
  return instance;
}

Questions

• Will a new version need to be released or is this a docs change? YES
• Which version should this be published as a part of? ASAP
• Does this impact the external API? YES
• Will it need to be a breaking change? NO

Check List

• All tests passing
• Docs updated with any changes or examples
• Added tests to ensure feature(s) work properly

Relevant Issues

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (v1.5.0@63587ec). Click here to learn what that means.
The diff coverage is 92.92%.

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[prescottprue]

Nice work! I have been wanting to do this for a while now. Going to test it out.

[prescottprue]

Overall looks awesome, just some small changes

[prescottprue]

It would be nice to see this as a const set to a function instead of a named function to limit scope unless there is a reason it is being named:

export default (firebase, config, dispatch) => {

[prescottprue]

It might help for clarity to call this file "createFirebaseInstance" or something along those lines.

[martynovs]

I've applied your changes

[prescottprue]

I believe the branch was made from master instead of v1.5.0.

Going to make similar changes and attempt to resolve conflicts.

[prescottprue]

Similar has been done and released in v2.0.0-alpha.

Hopefully will soon get time to try to get it into a v1.*.* version.