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>
@davidcelis I think @simi is right about this, can we please use the `@remove_const` trick and remove pry from the Gemfile at all?