Figure out a strategy to fire less (network) requests if the sync period (outOfDateAfter) is extremely fast

[superKalo]

Basically, in case the request response is not received yet, do not issue a new (network) request. Wait for the one which is still pending.

Here's a test for this (kind of extreme) use-case:

it('Should wait if there is a Promise pending and should NOT fire another one', done => {
    let networkRequestsCount = 0;

    const repo = new SuperRepo({
        storage: 'LOCAL_VARIABLE',
        name: 'test',
        outOfDateAfter: 1000, // 1 second
        request: () => {
            networkRequestsCount++;

            return new Promise(resolve => {
                clock.tick(10 * 1000);
                resolve('whatever');
            });
        }
    });

    repo.initSyncer().then( () => {
        expect(networkRequestsCount).to.equal(1);

        clock.tick(15 * 1000);
        expect(networkRequestsCount).to.equal(2);
    }).then(done, done);
});