Proposal: frint-data interop with Observable.from

[fahad19]

Currently

With frint-data, Models and Collections can be observed via .get$():

const todo$ = todo.get$();

Proposal

As it is done for frint-store via #393, it would be useful to make them interoperable with Observable.from as per the spec on TC39: https://github.com/tc39/proposal-observable#observablefrom

const todo$ = Observable.from(todo);