Allow images with data scheme (#4305)

* Add UnitTest for images

allows image elements with https scheme

* Test images with data scheme

* Add allowedSchemesByTag

* Fix error  Strings must use doublequote  quotes

src/core/components/providers/markdown.jsx

@@ -46,6 +46,7 @@ const sanitizeOptions = {
         "td": [ "colspan" ],
         "*": [ "class" ]
     },
+    allowedSchemesByTag: { img: [ "http", "https", "data" ] },
     textFilter: function(text) {
         return text.replace(/"/g, "\"")
     }