Eval whole clojurescript file without "already declared" exception

This is a work-in-progress pull at re-evaling a clojurescript file without getting a "namespace NS already declared" exception ([screenshot](https://www.dropbox.com/s/8fzreb5sue6fzbh/Screenshot%202014-11-01%2011.50.12.png?dl=0)). The current file eval [confuses users](https://groups.google.com/forum/#!searchin/light-table-discussion/already$20declared) and discourages us from having reload workflows like [figwheel](https://github.com/bhauman/lein-figwheel) does. This pull currently solves this by providing a command to eval a file's contents without the ns form. However,
I plan to extend this so that by default :eval uses the new behavior for cljs files. I realize this is not desirable for clojurescript files connected the LT-UI client since the LT eval is able to handle ns evals fine.

Things left to do on this pull:

* [ ] Strip ns form using cljs.reader/*
* [ ] Write a behavior for cljs :eval which delegates to :eval.no-ns unless editor is connected to the LT-UI client.

Feedback from cljs users welcome. @ibdknox If you have any concerns, I'm interested to hear them.