Add a class to help with limiting rates of events

[mxgrey]

This adds a simple utility class that helps limit the rate of events. This can be used to detect if a pathological cycle of conflict is happening.

[mxgrey]

A side-effect of this is we need to make rmf_utils a true shared library instead of only being an interface library.

[aaronchongth]

Works great! Thanks for making the changes to the library too! I will leave it un-merged waiting for the other PRs to be ready.

[mxgrey]

We can go ahead and merge this any time since it doesn't create any conflicts.