Refactor the Give Settings section

[DevinWalker]

Now that we have tabbed the main settings page, let's tab out the subsections too so it's less cluttered on each page.

[DevinWalker]

After reviewing this thoroughly I think we should reassess how our settings section is currently developed. CMB2 is pretty lackluster in it's ability to create settings pages. The new ability to toggle between tabs without page refresh is convenient but can potentially cause issues with other Add-ons. I propose that we develop a similar approach as Woo with an abtract class and
https://github.com/woothemes/woocommerce/blob/master/includes/admin/class-wc-admin-settings.php and various extended classes for the settings tabs: https://github.com/woothemes/woocommerce/tree/master/includes/admin/settings

Thoughts?

[DevinWalker]

After some heavy forking I decided this needs to be bumped from the currently scheduled milestone. It's a significant undertaking that will require lots of dev and testing.