Recreate monthly_total_precipitation_mv as a native matview

[corviday]

We'd like to change the construction of monthly_total_precipitation_mv (currently a table) to exclude cum_pcpn_amt and include instead pcpn_amt_pst24hrs as using cumulative precipitation totals to construct monthly statistics is throwing things off.

The first step will be to import monthly_total_precipitation_mv as a native matview managed by the ORM, then we can make a couple changes to variable inclusion.