Converted indendation to spaces, misc smaller fixes

As proposed in #9:

* Added .editorconfig (http://editorconfig.org)
* Touched all files, changing tabs to spaces, as also stated in the `.editorconfig` file (don't want to start a tabs vs. spaces flamewar here, this is just my preference, if it needs to be tabs, just let me know!)
* No further changes made, except for an added semicolon to Gruntfile.js (js-linting) and removing some unnecessary linebreaks in `galaxy/misc/_modals.scss`