My CMB2 additional field types

Some additional field types for the CMB2 meta box framework plugin.

Draft code

In my current client project I need some meta boxes with particular scopes and while CMB2 lacks little in term of field types and possibilities some fields I simply could not implement with the provided tools.
I've pushed a first version of the plugin to GitHub and, with a quick README.md copy and paste operation, that will define three additional field types

• tad_select2 - a select2 based select control
• tad_select2_action - a select2 based select control with a button beside it
• tad_sortable_list - a jquery-sortable powered list handler

The code has been produced in a day and is not polished and lacks any comment: I will iterate over it as the project goes on.