Update dependencies, add null control for Firestore tasks

Update gradle and fix error compilation

Merge pull request #69 from FrangSierra/development

Development

Merge pull request #65 from FrangSierra/development

Update dependencies and add basic implementation for Firebase Cloud F…

Merge pull request #60 from FrangSierra/development

Development

Merge pull request #56 from FrangSierra/development

Add new methods from the new Firebase releases and update README

Merge pull request #48 from FrangSierra/development

Proguard, listen queries and testing

Merge pull request #41 from FrangSierra/development

Merge development to Master

Update Dependencies

Indent all code
Add emitter.disposed control on onError calls

Include the rest of the new API methods