Improved dist pipeline

- Edited install instructions in Gruntfile.js
- Renamed "optimize" task to "createDistVersion"
- We now have a proper dist pipeline
- Added imagemin and htmlmin as optional tasks (I recommend using both!)
- Added usemin tags around `app.css` in `index.html`. Fixes #276
- Added support for using SCSS, LESS, Stylus and plain CSS at the same time. Mentioned in #276. After this commit every non main scss/less/styl file has to start with an underscore. (Partials) If not, then compiling takes longer :)
- Sorted dependencies in package.json, removed 'glob' because it's not used anymore
- Renamed `tmp/public` to `tmp/result` to avoid confusion.
- Made `Helpers.filterAvailableTasks` smarter: Fallbacks and improved dependency notation
- Deleted dom_munger config because it's unused
- Added compatibility for grunt-sass 0.8 (No file array in config)

It's all in one commit because I implemented everything at once. Next PR will be smaller, I promise ;)

Coming up next: Autoprefixer (Yeah, finally! I'm waiting for this myself :)