Create a constructor and parser for GraphQL "where" parameter

Problem/Motivation

Commercetools GraphQL provides the "where" parameter which it accepts as a string: https://docs.commercetools.com/api/predicates/query

Now we're composing it as string, but it's better to create a class that constructs it and generates a string.

Also, it should be able to parse the string to a structure, because we're receiving the "where" as string from FE queries and need to parse it to properly cache the operation.