Convert global settings to list subclass

[ryanhiebert]

The style is unclear and inconsistent about whether the settings are preferred to be lists or tuples. A discussion in the mailing list seems to indicate a consensus that lists are preferred, but backward compatibility may be a concern that needs to be considered.

I've implemented a ConfList list subclass that is able to act like a tuple in some tricky cases that might otherwise throw errors. Based on recent posts on the mailing list, the ConfList subclass is likely to be discarded in favor of simply documenting the backward incompatibility.

I updated the default template to use lists, and I've started working my way through the tutorial, and then on to the rest of the docs. There's still a bunch more to go through.

[carljm]

This looks really good! Thanks for the work! Since (as you noted) @freakboy3742 is comfortable doing this as a simple change without a deprecation path, and I am as well, I think I'll close this PR -- but if something crops up to convince us that a deprecation path is needed, we'll definitely resurrect this.

(Or if you want to extend this PR to complete hunting through the docs for tuple examples, and remove ConfList, I'll reopen it.)

[shacker]

Since a stated goal of moving from tuples to lists is avoiding the trailing comma problem in tuples, maybe remove the trailing comma from the list in the example?

[carljm]

There's nothing wrong with trailing commas; I think in multi line lists trailing commas are much preferable. The problem with tuples is the requirement of a trailing comma in a length-one tuple (which is likely not multi line).

[shacker]

No, nothing wrong with them. I was just surprised to see this after reading the django-developers thread, since half of the impetus for this change is to prevent the missing trailing commas problem with tuples. Just a minor observation. Fine either way.