Recursively check whether GraphQLQueryTree.name is part of EntityMetadata.propertiesMap

[Migushthe2nd]

Fixes #11

This makes it so that the recursive query builder also checks for all sub-fields whether the graphql field is actually part of the entity's propertiesMap.
Line was taken from:

perch-query-builder/src/classes/PerchQueryBuilder.ts

Line 26 in 3b4bebf

const validFields = tree.fields.filter(item => repository.metadata.propertiesMap[item.name] || item.fields.length > 0);