Add a simple `lotus console` command

`lotus console` will spawn an IRB (or Pry, if bundled) session that
loads the application code. This is a very basic analogue to `rails
console` and would be nice for testing out code ideas or modifying the
database.

Signed-off-by: David Celis <me@davidcel.is>
Also, any advice about testing Pry's presence? This is one thing I've struggled with in the past; as soon as we add Pry as a development dependency, it's just requirable everywhere and then the `IRB` case isn't detected.