Clean up BufferPool profile counters

We should clean-up the profile counters that are added to each node so that irrelevant info is hidden and relevant info is easy to find:

• Hide the limit if it is MAX_INT64
• Remove the BufferPool prefix and move into a "Buffer pool" section, or similar
• Remove or rename potentially confusing counters, e.g.
  • the cumulative allocation counters should be removed or renamed to be clearer that they are cumulative
  • PeakUnpinnedBytes is confusing unless you understand the internals