Avoiding closure created by coffeescript compiler for list comprehension returned result.
Adding general mechanism for overriding any setting for a channel when creating a channel.

All flags that we used in the past should be ported to this mechanism
in the future.
Added possibility of wrapping injected widget in a container.

Useful for lists which take their elements out of the DOM whenever they
are not in the viewport anymore.
Preventing multiple scrolls with the same params which triggers false positive no_data.
First time fetch management was moved in callback for post-processing items after they arrive in the channel.
Only count non-streampoll fetches when modifying last_fetch in a channel.

This is because the existence of last_fetch for a channel in Mozaic is
a marker that that channel has fetched data successfully. If we would
do this for streampolls it would break the assumption.
Code for post-processing was moved in callback for afterChannelDataArrived.
If channel is empty and a successful streampoll arrived, flush the channel buffer directly.
Added example for subscribing both to whole channel events and to individual model events in the same widget.
Modifying the CSS of widgets with data-wrapped whenever they have been rendered.

This is useful for widgets with data-delay=true which are wrapped in a
DOM element so that we only take the fixed height for their container
after they are fully rendered.
scrollable_widget now supports global window scroll and scroll localized to its container.
Simplifying channel init data because start_immediately doesn't exist anymore.

(it had only one use-case which was non-essential and it was
complicating DataSource too much)
initialize and destroy should be fat-arrowed.
Avoid implicit return of references.
Add method for cleaning up references to DOM elements from the widget.

Final goal is to minimize the number of detached DOM elements which
remain in memory.
Style changes to code which reports wrongful termination of widget too early.
Correctly undelegating Backbone.View events from the widget's DOM.
Avoid detaching the same widget twice due to widget_starter async problems.