Various improvements based on real-world usage

[psihius]

Implemented InStock filter Added 3 level deep nesting support for Option filtering Added live elastic index updates via Doctrine listener And other changes

[pamil]

Wow, thanks again, it's incredible! 🎉 Tests are failing though :(

[psihius]

Yeah, tests are failing, I had a glance, I think that's mostly a method signature fail. I'm gonna look at it tomorrow morning and try fix it.

[psihius]

Okay, this is getting out of hand, I have fixed everything I could find, did some major work and this PR should be merged before any other work is done. @pamil can you please take care of this? And check that I have merged your changes correctly, there were some conflicts.

[psihius]

@pamil @pjedrzejewski @lchrusciel Please review, done with all requested changes and a few adjustments/fixes

Travis build is failing due to some weird error, I don't have this one on my side and it's during installation phase.

[psihius]

Fixed travis failing due to stability settings of composer.json :)

[pamil]

Thanks @psihius, that's a really enormous amount of work! 🥇

[psihius]

Y'r welcome :)