[ADF-1312] form validation enhancements (#2180)

* validation api enhancements

- changing 'required' causes re-validation of the form
- get field by id

* allow binding field validators from html

* demo validator

* documentation updates

* fix after rebase

* markdown fixes

* markdown linter settings for workspace config (vs code)

* restore material theme

.vscode/settings.json

@@ -9,5 +9,15 @@
         "**/.happypack": true
     },
     "editor.renderIndentGuides": true,
-    "tslint.configFile": "ng2-components/tslint.json"
+    "tslint.configFile": "ng2-components/tslint.json",
+    "markdownlint.config": {
+        "MD032": false,
+        "MD004": false,
+        "MD024": false,
+        "MD009": false,
+        "MD013": false,
+        "MD036": false,
+        "MD033" : false,
+        "MD031" : false
+    }
 }