make maybe mutation queries case insensitive

[fengelniederhammer]

resolves #797

• Breaking change: throw "bad request" when there is unmatched variant query parser input
  • Stop logging unmatched parser input to stdout.
• make "maybe" case-insensitive in both, variant queries and normal mutation filters

PR Checklist

• [ ] All necessary documentation has been adapted.
• [x] The implemented feature is covered by an appropriate test.