Add batch activity partial update

[mircea-cosbuc]

No description provided.

[tbarbugli]

perhaps try and rewrite it as

activityPartialUpdate: function(data, callback) {
    return activitiesPartialUpdate([data]).then((response) => {
        return response[0];
    })
}

activitiesPartialUpdate: function(changes, callback) {
    // ...
}