Also, more consistently propagate a given checksum, which can
happen more through the `pkg-install' export from `pkg/lib'
than through `raco pkg'.
Also, report to the user when consulting GitHub or downloading
a checksum.
This termonology change affects lots of function names from `pkg/lib'
and `pkg/db' (former `pkg/pnr-db'), and it also affects some `raco
pkg' commands.
Existing package installations that are marked as 'pnr in a
local configuration are converted automatically to 'catalog, but any
existing "indexes" configuration must be changed to "catalogs".
