Add utility functions for writing Thrift REPLs

Summary:
This library allows writing Python scripts that connect with a running service, registered on Zookeeper, so you can interactively query it.

There's an example in finagle_service.py, but I anticipate most projects will customise it a bit.

Test Plan:
Opened a betslip in Ricardo like so:
```
vanguard:thrift-utils nicholas$ python -m fr_thrift.finagle_service --service-name=ricardo-service --thrift-file=/Users/nicholas/Code/Ricardo//ricardo-api/src/main/thrift/common.thrift --service-mode=nick

[...]

In [1]: from common import RicardoService

In [2]: from common.ttypes import GamePrices

In [3]: bt = GamePrices.ttypes.BetType(name="HcpOverBT", totalGoals=2.0, back=True)

In [4]: client = RicardoService.Client(protocol)

In [5]: client.openBetslip(506220, bt, None)
Out[5]: '4405255ebaca8f4e0607ee054ae33e52'
```

Reviewers: lasseb

Differential Revision: http://phabricator.cloud.footballradar.net/D881
Fix typo
Address style comments