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",