Cast JSON response in Python into appropriate object

[alphaville]

Currently OptimizerTcpManager.call returns a dictionary. We should convert the response of the TCP server into an appropriate object.

We will need some classes, such as (indicatively):

• SolverStatus (status of the solver, exit flag, solution, number of inner/outer iterations, etc)
• SolverError
• SolverResponse, which will store either a SolverStatus or a SolverError and will be equipped with methods like is_ok(), is_err() and get_solver_status() / get_solver_error() (or simply get())

[chutchi2]

@alphaville, would you like me to see if I can knock this out?

[alphaville]

@chutchi2 thank you very much for your interest, but this is almost complete in PR #144. Would you be interested in #114?

[chutchi2]

@alphaville sure!