Extension compiler pass

[Taluu]

Move all related stuff to DIC configuration into compilers ; basically, here what was done :

• Ensured that a broker (or channel_factory ? There are some naming issue I guess) can be declared as one if it has a swarrot.broker tag. This name can be modified though (swarrot.channel_factory ?)
• Ensured that a channel_factory implements the FactoryInterface
• Ensured that the PECL factory is not the only one used when building commands

That is more or less a POC, even though I added some tests.

(Related to #1)

[Taluu]

After several rebases and tests, I think this should do the trick. Poke @odolbeau.

[odolbeau]

As I said before, for now it's more a POC than a fully working version.

I think adding a CompilerPass for providers is a bit overkill for now.
For commands, why not, but before that, I would like to have a working and flexible version.

I think I will push to prod a sf2 worker with this bundle today or maybe tomorrow morning. After that, I will work on a way to configure easily which processors should be used for each consumers. :)

I hope I will be able to relase a first version before the end of the week. :)

[Taluu]

I wasd thinking that the ConsumerCommand Pass was a bit overkill rather than the ProviderPass. the ProviderPass is useful to allow any type of factory (even when we want to create another factory that is not registered and acknowledged within the bundle), because a tag is involved, which make it way easier to create a new factory.

Actually, the bundle is limiting the possibilities as this is hard coded into the configuration tree...