Added cache invalidation functionality

[HuFlungDu]

Invalidate GetNodeRightsCache entries when a user's permissions on a device or mesh.

This is a proposal for #7274.

In short, changing permissions can invalidate cache values, causing some users to not get permissions they should, or causing a user to continue having permissions for 10 seconds after they are removed from a device/mesh.

This version uses a hierarchal cache in order to allow cache invalidations for various scopes (user, mesh, device). The upside is that it allows us to empty the cache selectively based on what permissions are modified. Downside is the cache lookup is a bit more complicated (time should be about the same since there's no strcat happening), and cache invalidation of the entire user needs to iterate over all its children in order to do a correct cache count manipulation. This could be avoided if we were just fine with cache count being wrong and flushing slightly more often, but I didn't want to make that executive decision.

[si458]

if you happy for me to merge this then plz change to ready :)

[HuFlungDu]

I guess I prefer this solution.