Mark legacy JavaScript docs as deprecated

docs/en/02_Developer_Guides/15_Customising_the_Admin_Interface/02_CMS_Architecture.md

@@ -156,6 +156,11 @@ correctly configured form.
 
 ## JavaScript through jQuery.entwine
 
+__Deprecated:__
+The following documentation regarding Entwine applies to legacy code only.
+If you're developing new functionality in React powered sections please refer to
+[ReactJS in SilverStripe](./How_Tos/Extend_CMS_Interface.md#reactjs-in-silverstripe).
+
 [jQuery.entwine](https://github.com/hafriedlander/jquery.entwine) is a thirdparty library
 which allows us to attach behaviour to DOM elements in a flexible and structured mannger.
 It replaces the `behaviour.js` library used in previous versions of the CMS interface.

docs/en/02_Developer_Guides/15_Customising_the_Admin_Interface/03_CMS_Layout.md

@@ -2,6 +2,11 @@ title: Admin Layout
 
 # CMS layout
 
+__Deprecated:__
+The following documentation regarding JavaScript layouts applies to legacy code only.
+If you're developing new functionality in React powered sections please refer to
+[ReactJS in SilverStripe](./How_Tos/Extend_CMS_Interface.md#reactjs-in-silverstripe).
+
 The CMS markup is structured into "panels", which are the base units containing interface components (or other panels),
 as declared by the class `cms-panel`. Panels can be made collapsible, and get the ability to be resized and aligned with
 a layout manager, in our case [jLayout](http://www.bramstein.com/projects/jlayout/). This layout manager applies CSS

docs/en/02_Developer_Guides/15_Customising_the_Admin_Interface/04_Preview.md

@@ -2,6 +2,11 @@
 
 ## Overview
 
+__Deprecated:__
+The following documentation regarding JavaScript layouts and Entwine applies to legacy code only.
+If you're developing new functionality in React powered sections please refer to
+[ReactJS in SilverStripe](./How_Tos/Extend_CMS_Interface.md#reactjs-in-silverstripe).
+
 With the addition of side-by-side editing, the preview has the ability to appear
 within the CMS window when editing content in the _Pages_ section of the CMS.
 The site is rendered into an iframe. It will update itself whenever the content

docs/en/02_Developer_Guides/15_Customising_the_Admin_Interface/06_Javascript_Development.md

@@ -6,6 +6,11 @@ summary: Advanced documentation about writing and customizing javascript within
 The following document is an advanced guide on building rich javascript interactions within the SilverStripe CMS and
 a list of our best practices for contributing and modifying the core javascript framework.
 
+__Deprecated:__
+The following documentation regarding jQuery, jQueryUI and Entwine applies to legacy code only.
+If you're developing new functionality in React powered sections please refer to
+[ReactJS in SilverStripe](./How_Tos/Extend_CMS_Interface.md#reactjs-in-silverstripe).
+
 ## jQuery, jQuery UI and jQuery.entwine: Our libraries of choice
 
 We predominantly use [jQuery](http://jquery.com) as our abstraction library for DOM related programming, within the

docs/en/02_Developer_Guides/15_Customising_the_Admin_Interface/How_Tos/CMS_Alternating_Button.md

@@ -62,6 +62,11 @@ Here we initialise the button based on the backend check, and assume that the bu
 
 ## Frontend support
 
+__Deprecated:__
+The following documentation regarding jQuery, jQueryUI and Entwine applies to legacy code only.
+If you're developing new functionality in React powered sections please refer to
+[ReactJS in SilverStripe](./Extend_CMS_Interface.md#reactjs-in-silverstripe).
+
 As with the *Save* and *Save & publish* buttons, you might want to add some scripted reactions to user actions on the
 frontend. You can affect the state of the button through the jQuery UI calls.