The LnAddr, lndecode and lnencode naming didn't imply that it is
bolt 11 specific, making it confusing to work with, now that there are
also bolt 12 "lnaddr".
Renaming it to *bolt11* creates a clear separation to bolt 12 things and
reduces mental load.
This commit is pure renaming (using the PyCharm IDE refactor function),
except for the removal of the `object` inheritance of LnAddr/BOLT11Addr,
this is Python 2 legacy.
f321x