Rebrand step 1: s/riot/element/ in the places where it's reasonably simple

package.json

@@ -1,10 +1,10 @@
 {
-  "name": "riot-desktop",
-  "productName": "Riot",
+  "name": "element-desktop",
+  "productName": "Element",
   "main": "src/electron-main.js",
   "version": "1.6.6",
   "description": "A feature-rich client for Matrix.org",
-  "author": "New Vector Ltd.",
+  "author": "Element Communications Ltd.",
   "repository": {
     "type": "git",
     "url": "https://github.com/vector-im/riot-desktop"
@@ -82,9 +82,9 @@
     "linux": {
       "target": "deb",
       "category": "Network;InstantMessaging;Chat",
-      "maintainer": "support@riot.im",
+      "maintainer": "support@element.io",
       "desktop": {
-        "StartupWMClass": "riot"
+        "StartupWMClass": "element"
       }
     },
     "mac": {
@@ -103,9 +103,9 @@
     "afterSign": "scripts/electron_afterSign",
     "protocols": [
       {
-        "name": "riot",
+        "name": "element",
         "schemes": [
-          "riot"
+          "element"
         ]
       }
     ]