Query Grammar Fixes

[sebbader-sap]

Solve #477

[mhrimaz]

I think this requires more consideration.

<selectStatement> ::= "$select" <ws> "id" <ws>

<ws> ::= ( " " | "\t" | "\r" | "\n" )*

Following this grammar both $select id and $selectid will be valid inputs.
Whitespaces should be mandatory in some places and optional in other places.

[sebbader-sap]

Following this grammar both $select id and $selectid will be valid inputs.

Yes, that's of course correct. However, as the grammar is intended only as a logical expression of queries, this is acceptable. The syntactic validation of queries must happen on JSON level.