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/package.json

@@ -57,6 +57,7 @@
     "@ohif/ui": "^2.0.0",
     "@types/react": "^16.0.0",
     "classnames": "^2.2.6",
+    "config-point": "^0.3.4",
     "core-js": "^3.16.1",
     "cornerstone-math": "^0.1.9",
     "cornerstone-tools": "6.0.2",

platform/viewer/public/theme/theme.json5

@@ -0,0 +1,3 @@
+{
+  // Currently empty because nothing is configurable yet with themes
+}

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,