platform: implement NMPObject and NMPCache
NMPObject is a simple "object" implemenation around NMPlatformObject. They are ref-counted and have a class-pointer. Several basic functions like equality, hash, to-string are implemented. NMPCache is can be used to store the NMPObject. Objects are indexed via their primary id, but there is also multi-lookup via NMCacheId and NMMultiIndex. Part of the implementation is inside "nm-linux-platform.c", because it depends on utility functions from there.
This commit is contained in: