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>
I can do that; but it will end up preventing the `IRB` case, since `require 'pry'` won't end up triggering the `LoadError`. But perhaps it's better to test the Pry case and assume IRB is going to keep working like expected (which I'd agree with)