feat: Add theme/config-point capability and docs. (#2641)

This is the initial addition of the config point settings to allow run time loading of GUI settings via "theme" files/parameters.
The intent is to add an example PR that shows when to use config point, how to configure it, write documentation for it etc.

platform/viewer/src/appInit.js

@@ -17,6 +17,7 @@ import {
   errorHandler
   // utils,
 } from '@ohif/core';
+import ConfigPoint from 'config-point';
 
 /**
  * @param {object|func} appConfigOrFunc - application configuration, or a function that returns application configuration
@@ -49,6 +50,10 @@ function appInit(appConfigOrFunc, defaultExtensions) {
     appConfig,
   });
 
+  // Load the default theme settings
+  const defaultTheme = config && config.defaultTheme || 'theme';
+  ConfigPoint.load(defaultTheme, '/theme', 'theme');
+
   servicesManager.registerServices([
     UINotificationService,
     UIModalService,