Selecting a custom implementation of an extensible point

[leonardofl]

Currently the user can write a new CloudProvider or NodeSelector.
But if he write the name of his custom class in the properties file, DeploymentManager will not be able to select his class.
We must enable it.
We must also ensure the user can use his own custom ContextSender and RecipeBuilder.

[leonardofl]

Obs: Since ServiceType and ArtifactType are intended to be extended,
they cannot be simple enums.
Solution (by Carlos Moraes): to use the type safe enum pattern.
Create a class ServiceType, that has a private constructor
and initializes a set of instances based on a config file.
Default values can have constants pointing to them (e.g. SOAP = new ServiceType('SOAP')),
but to access non-defualt values it is necessary something like
ServiceType.getInstanceByName("JMS").

[leonardofl]

Done to NodeSelector: 18d67dd