Use javax.ws.rs constants instead of raw Strings.
Use else-if, instead of multiple if.
Add Logger and replace prints.
Add Produces annotation if there is an annotated return type.
Add XML annotations.
Add proper XML namespace.
Avoid returning null in API MethodMapper.
Add XML annotations.
Better logging.
Merge branch 'master' of https://github.com/dana-i2cat/mqnaas into api/improvements

Conflicts:
	api.rest/src/main/java/org/mqnaas/api/writers/InterfaceWriter.java
Remove console output and use logger.
Add missing annotation.
Treat one XMLRootElement annotated parameter methods.
Mark cases for body parameters to be fixed.
Use Cube Collection wrapper class until a better solution appears.
Mark cases for return types to be fixed.
Use Cube Collection wrapper class until a better solution appears.
Merge branch 'master' of https://github.com/dana-i2cat/mqnaas into api/improvements

Conflicts:
	core/src/main/java/org/mqnaas/core/impl/slicing/Slice.java
	extensions/network/itests/src/test/java/org/mqnaas/extensions/network/itests/NetworkManagementTest.java
	extensions/network/network.impl/src/main/java/org/mqnaas/network/impl/Slice.java
Merge pull request #137 from logoff/api/improvements

REST API improvements and bugs