Fix accounts_proposed subscription receives twice message

[cindyyan317]

Client will receive two identical messages if their subscription's accounts_proposed has new transactions.
The old code traversed all the field in the transactions, Trying to convert it to account, then send the update accordingly.
For payment transaction like this:
{
"Account":"rh1HPuRVsYYvThxG2Bs1MfjmrVC73S16Fb",
"Amount":"40000000",
"Destination":"rDgGprMjMWkJRnJ8M5RXq3SXYD8zuQncPc",
"Fee":"20",
"Flags":2147483648,
"Sequence":13767283,
"SigningPubKey":"036F3CFFE1EA77C1EEC5DCCA38C83E62E3AC068F8A16369620AF1D609BA5A620B2",
"TransactionType":"Payment",
"TxnSignature":"30450221009BD0D563B24E50B26A42F30455AD21C3D5CD4D80174C41F7B54969FFC08DE94C02201FC35320B56D56D1E34D1D281D48AC68CBEDDD6EE9DFA639CCB08BB251453A87",
"hash":"F44393295DB860C6860769C16F5B23887762F09F87A8D1174E0FCFF9E7247F07"
}

"SignlingPubKey" can be converted to account too, in this case, the account's update will be sent twice.

The fix is to not to use public key convert.
We previously did not use the real transaction json, not really cover the code "RPCHelper.cpp", also add the real json to unittest.

[godexsoft]

Awesome! 💥🚀

[codecov]

Codecov Report

Merging #672 (4e0bcd2) into develop (244337c) will increase coverage by 0.32%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #672      +/-   ##
===========================================
+ Coverage    29.92%   30.25%   +0.32%     
===========================================
  Files          140      140              
  Lines         7431     7436       +5     
  Branches      4420     4422       +2     
===========================================
+ Hits          2224     2250      +26     
+ Misses        3137     3109      -28     
- Partials      2070     2077       +7     

see 2 files with indirect coverage changes