Strict types, Variants, Options and Product population

[psihius]

Implemented strict_types across the plugin. Added Product variants and options to the elastic index Updated ProductDocumentFactory to create Variants and Options and push those to Elastic.

[psihius]

Well, this ended up being a bit messy, especially because we both changed the ProductDocumentFactory and it turned out into a lot of merge conflicts, so I had to push in all my changes, otherwise this PR was unmergeable. There are a few things we talked over with @pamil and after this is merged I will create a new PR and this time will make sure I keep it small.

[psihius]

Tests are not in a very good place right now and I think we need @Arminek to help us out here a bit :) But I updated shop.yml fixtures - added product variants and product options and product option values to the mix, so we can test those too now.

PR is extending a lot here - adding support for variants, in stock filter, options filter, a few fixes by override for the FilterManagerBundle (there are things that just are plain wrong) and creates a few new filters because they require more than 1 nested level handling.

[psihius]

@lchrusciel @pamil ready for review, fixed so tests work. More work will be done on this in future PR's

[pamil]

Thanks @psihius, amazing work! 🎉