Mainstem / nhdplusV2 comid lookup

The mainstem IDs are more or less final now. We need to check in a look up table for posterity. From not on those IDs can be used like name identifiers rather than as level paths.

https://code.usgs.gov/wma/nhgf/gfv2.0/-/commit/59caf1914752cd53559ffb89942a5e6e39e60208

closed