Break down json_parser.h/cpp

[brejski]

json_parser grew out of control to become a one big monster with tons of API representing different level of granularity (low level generic json parsing to very specific cosmos message parsing APIs).

We should move some of the higher level APIs to a new file.

[jleni]

is this still relevant?

[brejski]

Yes, it's part of the cleanup. json_parser contains transaction parsing code which should really be moved to another file.

[brejski]

Issue has been fixed now.