BOOKKEEPER-941: Feature Switches for controling client and server behavior

- Introduce Features that are dynamic configuration options
- Allow specifying Features as configuration parameters

This is a port of the feature switches following changes
https://github.com/twitter/bookkeeper/commit/c2a092ab9b585f1d30d9e9b9dead0533efa49855
https://github.com/twitter/bookkeeper/commit/f9762d126e311a6b129e6e169dc62c2a0bdb7b4a

Author: Robin Dhamankar <robindh@Robins-MacBook-Air.local>

Reviewers: Matteo Merli <mmerli@apache.org>, Sijie Guo <sijie@apache.org>

Closes #54 from robindh/FeatureSwitches
7 files changed