Allow 'edit self' and 'reload-code self'

This didn't work due to a quirk in Pry::CodeObject.lookup() which purposely ignores 'expressions'
as they can be methods, which are dangerous to lookup. We now make an exception when the expression is 'self'

This code needs to be refactored as we have ridiculosu method names like  `def variable_or_constant_or_self?`
and we have methods like this in a couple of places. Refactor pls.