feat: multi slot levels in components

[Tahul]

Reporting conclusions from this PR:

#432

Atinux:
I removed the usage of the HeroTemplate wrapper, it seems that multi slots levels does not work (not really a surprise), cc @farnabaz so you know we have this issue, but we can investigate after this week :)

Farnabaz:
About the multi level slot, this is expected, since <Markdown> looks lots in parent component.
There is a node props in <Markdown> that users can pass slots directory to it
OR
we can walk through parents and find the right slot

From my perspective, using Node props from Markdown should be great, but maybe this needs to be documented.

I will document the API part once we are done with NuxtJS.org of course.