Reorder the monad transformers in the Idris monad to allow completion

I'm working on improving tab completion in the Idris REPL. I wanted to send this right now to prevent too much divergence over time, as it did a fairly drastic change.

Completion of names will require access to the interpreter state. Unfortunately, the stacking order of the monad transformers didn't allow this. This has been changed. As a side effect, when get was used to access the state, it has been consistently replaced with getIState.

The standard library typechecks with no problems following this change.