Add global settings

I use Manual Crop on a few different image fields, and on each one I have to configure the same settings. I'd like to be able to configure some global settings (at /admin/config/media/manualcrop) that determine how Manual Crop will function on all image fields.

Now only certain settings will work in a global scope (such as keyboard shortcuts and inline cropping). Other settings will need to stay on individual field's configuration forms (such as enable and styles list).

Also, there will obviously need to be the ability for fields to override the global settings on an individual basis.