Issue 31: Update cli entrypoints, use sub commands within a flowalert entrypoint

Based on the specs in issue #31 (closed) the subcommands now appear as:

flowalert top level commands

config sub commands

debrisflow sub commands

Areas that might need some clarification

1. There are currently no sub-commands for process
2. The specs specify that update is a subcommand of debrisflow, but from the code the modify (previously modify-fire) method goes with the other debris flow commands. Should the update command (which updates rainfall data) be a subcommand of a category?

NOTE 1 I did not change the internal code within the commands unless I saw an issue that needed to be addressed while writing tests. NOTE 2 Since we have not decided on the method to mock reaching out to the internet (mock.patch vs vcrpy) the tests written do not reach out do not reach out to the internet.

closes #14 (closed)

closes #31 (closed)

closes #32 (closed)