Implement Virtualchassis

[kuhball]

This MR attempts to close #66.

The following has been done:

• Add a new function virtualChassisMaster to with the hardcoded filter virtual_chassis_member=True&vc_position=1 within netbox
• Add a new function virtualChassis to fetch virtualchassis
• Extend the getLinkedObjects function to combine the interfaces of all virtual chassis members

The idea is to fetch all the data like primary_ip, contact etc. from the first device in the virtual chassis and combine the interfaces over all chassis members. This is similar to the way netbox handles virtual chassis in the UI.