Fix UnknownFObjectParser and add unit tests

[lchanmann]

Ref

• https://nanopay.atlassian.net/browse/NP-11968

Tests

UnknownFObjectParserTest
         ✓ SUCCESS: Parsed json, input:{"key":"value","key2":true,"key3":null,"key4":{"foo":"bar"},"key5":[true,false,null,"text",1.23]} 
         ✓ SUCCESS: Parsed empty json, input:{} 
         ✓ SUCCESS: Parsed json with un-quoted key, input:{key:"}"} 
         ✓ SUCCESS: Parsed json with comment above properties, input:{//comment1 \n key:"1",//comment2 \n key2:"2"} 
         ✓ SUCCESS: Parsed empty json with just comment, input:{// comment1 \n  // comment2 \n} 

TEST REPORT SERVER - TEST CASES: 1, TESTS: 5 (PT0.57S)
 PASSED: 5 
 FAILED: 0