Qualified imports

e.g.

``` haskell
module M1 where
  
  trace x = x

module Main where

  import Prelude
  import Control.Monad.Eff
  import M1
  import qualified Debug.Trace as T
  
  main = T.trace (trace "hello")
```

Currently only supports `import qualified X as Y`, can't use `qualified` or `as` on their own yet.