Add list support for :variable/type

[r0man]

Hello @macluck,

I would like to use list types in my GraphQL variables, but it looks like venia doesn't support this yet. This PR adds support for this.

Would you like to merge this?

Roman

[brownsf]

this would be a big help for me

Any idea on a timetable?

[stevebuik]

this would be useful for me as well. Thanks @r0man for the impl.

[r0man]

@stevebuik I recently built another query language for graphql. you may find this useful. it should support your use case. https://github.com/r0man/grafeo

[stevebuik]

Cool. I'll give it a side-by-side try.