Support more recent AKCP MIBs

[lunkwill42]

Is your feature request related to a problem? Please describe.
A customer has installed 7 new environment probes from AKCP (SensorProbe SP2+). These appear to use a revision of the AKCP MIB that is not compatible with the existing NAV implementation.

Describe the solution you'd like
The revised MIB should be supported by NAV, analogous to the old revision.

Additional context
The customer submitted a MIB file, which was made available in a probe software release by the vendor:
akcp.mib.txt

[lunkwill42]

It appears the revised MIB mostly introduces new object trees for the new models (e.g. plusSeries OBJECT IDENTIFIER ::= { akcp 3 }) - we might get away with just updating the Pythonized smidump of the MIB and add code to fetch sensor data from the new tree.