Feature: Change markdown engine to markdown it

This commit removes the old evilstreak markdownjs engine.

- Adds specs to WhiteLister and changes it to stop using globals
    (Fixes large memory leak)
- Fixes edge cases around bbcode handling
- Removes mdtest which is no longer valid (to be replaced with
    CommonMark)
- Updates MiniRacer to correct minor unmanaged memory leak
- Fixes plugin specs

plugins/discourse-details/test/javascripts/lib/details-cooked-test.js.es6

@@ -8,7 +8,7 @@ const defaultOpts = buildOptions({
     emoji_set: 'emoji_one',
     highlighted_languages: 'json|ruby|javascript',
     default_code_lang: 'auto',
-    censored_words: 'shucks|whiz|whizzer'
+    censored_words: ''
   },
   getURL: url => url
 });
@@ -19,17 +19,13 @@ test("details", assert => {
     assert.equal(new PrettyText(defaultOpts).cook(input), expected.replace(/\/>/g, ">"), text);
   };
   cooked(`<details><summary>Info</summary>coucou</details>`,
-         `<details><summary>Info</summary>\n\n<p>coucou</p>\n\n</details>`,
+         `<details><summary>Info</summary>coucou</details>`,
          "manual HTML for details");
-  cooked(` <details><summary>Info</summary>coucou</details>`,
-         `<details><summary>Info</summary>\n\n<p>coucou</p>\n\n</details>`,
-         "manual HTML for details with a space");
 
-  cooked(`<details open="open"><summary>Info</summary>coucou</details>`,
-         `<details open="open"><summary>Info</summary>\n\n<p>coucou</p>\n\n</details>`,
-         "open attribute");
-
-  cooked(`<details open><summary>Info</summary>coucou</details>`,
-         `<details open><summary>Info</summary>\n\n<p>coucou</p>\n\n</details>`,
-         "open attribute");
+  cooked("[details=testing]\ntest\n[/details]",
+`<details>
+<summary>
+testing</summary>
+<p>test</p>
+</details>`);
 });