add coffee files

Create `coffee` files from all `javascript` files in `core/`. Many of these `coffee` files were manually edited for readability and to fix some issues the `coffee` compiler couldn't deal with, mainly `.bind(this)` and 'return' at the end of functions that was unnecessary.
The files that are manually edited for issues are:
`workspace.coffee`
`forceSliders.coffee`
`keyListener.coffee`
`linkHistogram.coffee`
`selection.coffee`

I removed all the `javascript` files in `core/` from the repository. They are also ignored now so their changes won't affect the repository.


__Note__

If you don't have `coffee` installed, run `sudo npm install -g coffee-script`
To develop locally, run `coffee --watch --compile -o core/ core-coffee/` so that these `javascript` files are automatically compiled when you save its corresponding `coffee` file.