Add ability to set minimum crop size

Before this, user can crop the image to any size. The issue with
that is that if you are using paperclip and the cropped image is
smaller than what it needs, it will upsize those selections
resulting in low quality images.
Extend crop area to maximum possible width

Crop area now starts at maximum width such that users only have
to downsize until the crop suites their requirement, thus improving
user experience.
Update README.md
Added attr_accessible to model

Previously had to add it by hand, alongwith a long list of attributes
that papercrop was setting temporarily.
Update README.md
Include minified resources

Minified version of jcrop replaces standard jcrop saving 30kb.
Made compatible with Rails 4

- attr_accessible added only for Rails 3 and below
- adds the cropping_params helper
- Fixes #1
Documented Rails 4 helper in Readme.md
Changed cropping_params synta

- Updated Readme.md accordingly
- Fixes the bug in which prams.require.(:user) accidently got hardcoded
Merge branch 'ezuhaib/papercrop/master'
Updated jCrop to v0.9.12
Updated jCrop CSS to v0.9.12