Feature/scheduling capability

This patch includes the Scheduling capability for MqNaaS.

This capability provides the ability of scheduling the execution of a specific IService. User can define the parameters for the service execution and also the trigger that launches this execution.

Trigger defines when the execution would take place. Current implementation only contains the requirements for the CONTENT sprint, which is definining a simple implementation containing the starting date of the execution. However, its supposed to support more features in the future, like schedule repeated jobs.

Pull request contains the first implementation of the Scheduling Capability. It uses Quartz [1] as scheduling library. The main components of this library are the scheduler itself and the Job interface. The Job interface is implemented by our ScheduledJob class, which is the one using the ExecutionService to execute the scheduled services.

Even though the latest Quartz version is 2.2.X, we are forced to use 1.6 due to 2.x is not OSGIfied.

FIXES:
http://jira.i2cat.net/browse/OPENNAAS-1426
Move the inner checks of ServiceExecution to its constructor and throw an InvalidArgumentException