Added functionality and fixed bugs

The following functionality was added:

• Support for static ports definitions
• Added an option to remove serial number from tasks (serial numbers added for ZK persistency)
• Added a task launched event
• Support for task graceful restart (on the "boilerplate" side) by launching a duplicate and killing the task after the duplicate is healthy
• Added task health check support (both in Mesos and in the framework itself with events)

Fixes:

• Fixed issues when reconnecting to master
• Fixed an issue with large event messages not handled properly
• Fixed an issue with old tasks staying in the ZK and loaded.

Thanks @dudyk for contributing the code!