Support inputting arguments for GraphQL Variables

[danielmai]

In Ratel, the only way to run queries with GraphQL Variables is to pass the arguments as default values (e.g., $a: int = 10). It'd be useful to input arguments to a query without modifying the query itself.

[felixfbecker]

Yes, this makes it really difficult to copy-paste queries (need to manually replace all the variables with values)

[paulftw]

Query Variables UI is available in the dev builds. Please post feedback here

[paulftw]

Fixed in #210