feat: unblacklist img tags with data URIs

fixes vector-im/vector-web#1692

src/HtmlUtils.js

@@ -28,7 +28,7 @@ var sanitizeHtmlParams = {
         // deliberately no h1/h2 to stop people shouting.
         'h3', 'h4', 'h5', 'h6', 'blockquote', 'p', 'a', 'ul', 'ol',
         'nl', 'li', 'b', 'i', 'u', 'strong', 'em', 'strike', 'code', 'hr', 'br', 'div',
-        'table', 'thead', 'caption', 'tbody', 'tr', 'th', 'td', 'pre'
+        'table', 'thead', 'caption', 'tbody', 'tr', 'th', 'td', 'pre', 'img',
     ],
     allowedAttributes: {
         // custom ones first:
@@ -42,7 +42,9 @@ var sanitizeHtmlParams = {
     selfClosing: [ 'img', 'br', 'hr', 'area', 'base', 'basefont', 'input', 'link', 'meta' ],
     // URL schemes we permit
     allowedSchemes: [ 'http', 'https', 'ftp', 'mailto' ],
-    allowedSchemesByTag: {},
+    allowedSchemesByTag: {
+        img: [ 'data' ],
+    },
     
     transformTags: { // custom to matrix
         // add blank targets to all hyperlinks except vector URLs