Write guideline for data management

[HaGuesto]

Following #275 and #289,
a guide how to download data from firestore collections to local storage, how to update them and query the data locally has to be written.

@rubenspgcavalcante and @bfirsh please correct this issue if I am wrong.

[rubenspgcavalcante]

I still owing you guys a draft of my idea on this case. I'll get some time to work on this ok 👍

[rubenspgcavalcante]

Ok my Idea was this:

We can get information from firebase in case of the user is online, or just get the entire updated state (a simple JSON stored on localstorage) and use it as our initial state (no queries, no worries).
The observables is a must have to keep the app state up-to-date, so we don't have to do pooling (is horrible to maintain and costs a lot for the device, mainly mobile ones). I need to check on firebase docs further information about this tho.
All the joins we'll be made in our side, as we're going to have this entire information in our app state (redux store). Probably we'll create some aggregators to do the job and a simple HOC to pass this state data already joined.

All in all, this is the idea I was trying to explain on the meeting with @HaGuesto and @bfirsh :)