refactor checkpoint for LRU crawler

now has internal module system for the LRU crawler.

autocrawl checker should be a bit better now. doesn't
constantly re-run the histogram calcs.

metadump works as a module now. ended up generalizing the client case outside
of the module system since it looks reusable. Cut the amount of functions
required for metadump specifically to nothing.

still need to bug hunt, a few more smaller refactors, and see about pulling
this out into its own file.