Feature/vnmapper

The patch's goal is to map the SPF result to a OpenNaaS network topology. Therefore, the  MappingResultParser class has been created. The parsing method contains two steps:

1) Parse virtual devices: Virtual devices are linked by the "implementedBy" attribute to an existing device of the network model input. 

2) Parse virtual links: also virtual links are linked by the same attribute, but this attribute implements a new Path object containing existing links of the network model input. 

So, the resulting network model would contain:

- Virtual devices.
- Virtual links between the virtual devices.
- References to the devices and links of the algorithm model input. 

Integration tests for the capability has been implemented.