Added fallback on model.get()

[gsdevme]

Allows for a view, template etc to define a fallback if the attribute
is null or undefined … nice to have it other then undefined in the
rendered templates

[braddunbar]

Hi @gsdevme, thanks for the patch! If you're interested, this has been discussed previously a couple of times in #1184 and others.

There's really no need for a fallback for get. You can just use model.get('attr') || value instead, which is approximately the same number of keystrokes and very readable.