Replace markup-it with Remark for rendering markdown in the editor preview

package.json

@@ -101,6 +101,7 @@
     "dateformat": "^1.0.12",
     "deep-equal": "^1.0.1",
     "fuzzy": "^0.1.1",
+    "hast-util-to-html": "^3.0.0",
     "history": "^2.1.2",
     "immutability-helper": "^2.0.0",
     "immutable": "^3.7.6",
@@ -112,6 +113,7 @@
     "lodash": "^4.13.1",
     "markup-it": "^2.0.0",
     "material-design-icons": "^3.0.1",
+    "mdast-util-to-hast": "^2.4.0",
     "moment": "^2.11.2",
     "netlify-auth-js": "^0.5.5",
     "normalize.css": "^4.2.0",
@@ -157,6 +159,8 @@
     "redux-notifications": "^2.1.1",
     "redux-optimist": "^0.0.2",
     "redux-thunk": "^1.0.3",
+    "remark": "6",
+    "remark-html": "^6.0.0",
     "selection-position": "^1.0.0",
     "semaphore": "^1.0.5",
     "slate": "^0.14.14",