Add insertCallback, init radio value
Squashed commit of the following:

commit 061caf22c27805f1ecaeeffe7ce3083f2657b23a
Author: Huei Tan <huei90@gmail.com>
Date:   Thu Aug 14 13:22:44 2014 +0800

    Fix insertCallback location

commit d692348b0068bad143ee7864a7890f5868d64f3d
Author: Huei <huei90@gmail.com>
Date:   Wed Aug 13 11:44:30 2014 +0800

    Allow insertCallback paramter

commit a72952112b0d3dbda62f48cd0bc91f2daa4a5b6e
Author: Huei <huei90@gmail.com>
Date:   Wed Aug 13 11:24:51 2014 +0800

    Add insertCallback

commit 212d13dcaa204dfd5021ddde42856bad7b93851c
Author: Huei <huei90@gmail.com>
Date:   Fri Jul 25 17:01:07 2014 +0800

    update demo code and directive.js

commit 2e0905335a2ebad1a075416680c7525e922780f8
Author: Huei Tan <huei90@gmail.com>
Date:   Fri Jul 18 16:00:42 2014 +0800

    Fix checkbox init

commit 7429fc7b1474a1f120fca9febc90171a0ffa2aea
Author: Huei Tan <huei90@gmail.com>
Date:   Fri Jul 18 14:11:36 2014 +0800

    Fix initial radio value
Fix ie8 checkbox inputText issue
Merge branch 'master' of https://github.com/accuvally/angular-form-builder into gh-pages