Added RemoteConfig API

[Jeanmsilva89]

Re-added RemoteConfig feature.

[mikelambert]

It seems configValueForKey only gets the stringValue of an item?

Before I discovered firestack, I had built out a firebase3 module myself for the remoteconfig and analytics stuff I had needed. If you're motivated to get this implemented, perhaps you'd be interested in stealing my remoteconfig code?

https://github.com/mikelambert/react-native-firebase3/blob/master/android/src/main/java/org/jall/reactnative/firebase/RNFIRRemoteConfig.java

https://github.com/mikelambert/react-native-firebase3/blob/master/ios/Firebase/RNFIRRemoteConfig.m

It definitely works in iOS, and I'm pretty sure it works in Android (my app is broken w.r.t. this right now, but I believe that's due to the recent inclusion of both rn-firestack and rn-firebase3 in my project, both trying to initialize fb under-the-hood)

[SuperBesse]

Hi,
have you an idea when this PR will be available ?

[nkashyap]

+1 for both ios & android

[chatras]

When will this be available? Great work so far guys! Loving this library!

[matts2cant]

Hi ! Do you know when you plan on releasing this ?

[nkashyap]

Here is PR for v3

Salakar#12