added ability to store props on each image

now you can store props on each image for easy retrieval later, e.g. id
updated Gruntfile to minify original source

updated Gruntfile to minify original source, rather than a manually
created min.js

updated preloadr.min.js
forgot to add props on sequential load
Merge pull request #2 from HaykoKoryun/master

added some new features