Add micro gallery function for modal with images on page

Closes #35.
Minor clean up of Sass and JS
Overwrite IE8 hack for IE9 and 10 to get modal working without JS

The IE8 hack also targeted IE9 and IE10. By overwriting the
behavior using `:target` we can get the modal working in these
newer browsers without JavaScript too.

Closes #33.
Added LESS implementation of Modal CSS
Extended .gitignore
Added test-file for testing CSS compiled from LESS
Adjusted Gruntfile.js and package.json to integrate tasks for compiling LESS
Integrated latest changes from modal.scss into modal.less