Add a ELASTICSEARCH_DEFAULT_INDEX settings

[Atala]

This settings would enabled easy index overriding when testing.
What do you think about it?

[lauxley]

It indeed seems like a very good idea, thx.

[Atala]

Cool! I love the approach you've taken, it's pretty easy to use.

Two things I would like to ask:

• are you planning to package it properly as a django app?
• it would be very nice if the class EsIndexable wasn't inheriting from Model, but was a proper mixin (I don't what it would take to do that as it would be harder to plug reindexing signals/manager's logic)

[lauxley]

Thanks,
I will probably release it on pypy, but it's still pretty early in the dev phase and the code is not very stable yet, so even if the api is probably not going to change a lot, i'd rather wait to have a better test coverage and full docs at least.
Why do you want a mixin rather than a Model subclass ? If it's really a problem can you open an issue and explain why, a closed pr is not the best place to talk about it ;)