Add backuptask.js to work with new storage interface

package.json

@@ -14,10 +14,10 @@
   ],
   "dependencies": {
     "@sindresorhus/df": "^2.1.0",
+    "archiver": "https://registry.npmjs.org/archiver/-/archiver-1.3.0.tgz",
     "async": "^2.1.4",
     "aws-sdk": "^2.1.46",
     "body-parser": "^1.13.1",
-    "checksum": "^0.1.1",
     "cloudron-manifestformat": "^2.8.0",
     "connect-ensure-login": "^0.1.1",
     "connect-lastmile": "^0.1.0",
@@ -63,7 +63,7 @@
     "split": "^1.0.0",
     "superagent": "^1.8.3",
     "supererror": "^0.7.1",
-    "tar-fs": "^1.15.2",
+    "tar-fs": "https://registry.npmjs.org/tar-fs/-/tar-fs-1.15.2.tgz",
     "tldjs": "^1.6.2",
     "underscore": "^1.7.0",
     "valid-url": "^1.0.9",