Merge PR #66, use class button-disabled instead of disabled="disabled". Props @sc0ttkclark.

commit 3709e957c41a63d2399578da7b55b33fad011217
Merge: 1702e1d ce235de
Author: Justin Sternberg <justin@dsgnwrks.pro>
Date:   Mon Nov 17 10:54:24 2014 -0500

    Merge branch 'hotfix/issue-63' of https://github.com/sc0ttkclark/CMB2 into sc0ttkclark-hotfix/issue-63

    Conflicts:
    	js/cmb2.min.js

commit ce235ded77e8bd5e658ae1577d3d13678ad859f2
Author: Scott Kingsley Clark <lol@scottkclark.com>
Date:   Thu Oct 30 01:17:04 2014 -0500

    Check if remove button is disabled based on class, bail if so

commit c92e984e23aaedbee19d9d7bc6706c66944c011c
Author: Scott Kingsley Clark <lol@scottkclark.com>
Date:   Thu Oct 30 01:14:24 2014 -0500

    Use class button-disabled instead of disabled="disabled" for <a> buttons

    Also fix attr/removeAttr usage for 'disabled', 'checked', and 'selected'