Move email rendering to browser

the email preview no longer has a delay after each change. This also
avoids a race condition in which the email currently being edited could
be actually sent.

package-lock.json

@@ -12,6 +12,14 @@
         "regenerator-runtime": "^0.13.4"
       }
     },
+    "@ts-stack/markdown": {
+      "version": "1.3.0",
+      "resolved": "https://registry.npm.taobao.org/@ts-stack/markdown/download/@ts-stack/markdown-1.3.0.tgz",
+      "integrity": "sha1-OdkuDifo9w6Ba3L/EzaO6HWWe+o=",
+      "requires": {
+        "tslib": "^2.0.0"
+      }
+    },
     "@types/node": {
       "version": "14.14.16",
       "resolved": "https://registry.npm.taobao.org/@types/node/download/@types/node-14.14.16.tgz?cache=0&sync_timestamp=1608756036972&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2F%40types%2Fnode%2Fdownload%2F%40types%2Fnode-14.14.16.tgz",
@@ -228,9 +236,9 @@
       "integrity": "sha1-vfpzUplmTfr9NFKe1PhSKidf6lY="
     },
     "esbuild": {
-      "version": "0.8.49",
-      "resolved": "https://registry.npm.taobao.org/esbuild/download/esbuild-0.8.49.tgz",
-      "integrity": "sha1-PTP3GzlmYR+CLPTIOBFfP70W3vI="
+      "version": "0.8.50",
+      "resolved": "https://registry.npm.taobao.org/esbuild/download/esbuild-0.8.50.tgz",
+      "integrity": "sha1-6/JP3gza0aNpeJ3W/XqCCwoB5Gw="
     },
     "escalade": {
       "version": "3.1.1",
@@ -1463,6 +1471,11 @@
         "safe-buffer": "~5.1.0"
       }
     },
+    "tslib": {
+      "version": "2.1.0",
+      "resolved": "https://registry.npm.taobao.org/tslib/download/tslib-2.1.0.tgz?cache=0&sync_timestamp=1609887446200&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Ftslib%2Fdownload%2Ftslib-2.1.0.tgz",
+      "integrity": "sha1-2mCGDxwuyqVwOrfTm8Bba/mIuXo="
+    },
     "typescript": {
       "version": "4.1.3",
       "resolved": "https://registry.npm.taobao.org/typescript/download/typescript-4.1.3.tgz?cache=0&sync_timestamp=1609830171931&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Ftypescript%2Fdownload%2Ftypescript-4.1.3.tgz",