Netgen ibexa scheduled visibility

[petarjakopec]

testing instance: https://media-site-scheduled-visibility.dev9.netgen.biz/
Everything except docs and integration tests is here(will update it), for testing:
I added all parameters to dev config file, by default they are not necessary and mechanism is disabled.
For content to be applicable for this mechanism, it needs to have two fields with identifiers publish_from and publish_to that are either ezdate or ezdatetime. I created one new content type scheduled_visibility for testing. Here is example of its content:
https://media-site-scheduled-visibility.dev9.netgen.biz/adminui/view/content/780/full/1/555.
Parameters example(from dev instance):
parameters:
netgen_ibexa_scheduled_visibility.enabled: true
netgen_ibexa_scheduled_visibility.strategy: 'location'
netgen_ibexa_scheduled_visibility.content_types.all: true
netgen_ibexa_scheduled_visibility.content_types.allowed: []
netgen_ibexa_scheduled_visibility.sections.hidden.section_id: 4
netgen_ibexa_scheduled_visibility.sections.visible.section_id: 1
netgen_ibexa_scheduled_visibility.object_states.object_state_group_id: 2
netgen_ibexa_scheduled_visibility.object_states.hidden.object_state_id: 3
netgen_ibexa_scheduled_visibility.object_states.visible.object_state_id: 1

[pspanja]

@petarjakopec with the remaining remarks resolved, I'm pretty much out of ideas what to improve here. I'll test it on a bigger repo to see how performant it is. You can check if there is anything you would still want to improve from your side. And also update the docs, I didn't pay much attention to it so far.