Re-Implement caching for Performance Counter data

[LordHepipud]

With the Icinga PowerShell Framework we can access Performance Counters very easily, but have no possibility to cache objects yet to access them quicker on loaded daemons for example.

Expected Behavior

We should cache Counter objects to later access them quicker without having to re-create them always

This references to #11 as well

[LordHepipud]

This will also fix several issues with counters not having proper values and to always return 0 instead of the actual value.