[FIX] crash on getting payments for account

- if there were previously failed submitted payments ripple-rest would crash while trying to retrieve payments for a given account
- remove duplicate parsePaymentFromTx method
Merge pull request #125 from geertweening/develop

WIP: rework response handling
[FEATURE] Generate new wallet from /accounts/new
[TEST] Add test for accounts/new
[TASK] minor coding style optimizations
Merge pull request #128 from geertweening/fix/crash_on_get_payments

[FIX] crash on getting payments for account
[TASK] Use assertions in test and change spacing to follow style guide
Merge pull request #129 from AiNoKame/new-wallet

[FEATURE] Generate new wallet from /accounts/new
[TASK] adopt specced error types and status codes

and some cleanup