Compatibility with extensions API v2 - pending actual Python3 test

manifest.json

@@ -1,6 +1,5 @@
 {
-  "manifest_version": "1",
-  "api_version": "1",
+  "required_api_version": "^2.0.0",
   "name": "Remmina",
   "description": "Quick access to Remmina profiles",
   "developer_name": "noam09",

versions.json

@@ -0,0 +1,4 @@
+[
+  { "required_api_version": "^1.0.0", "commit": "v1" },
+  { "required_api_version": "^2.0.0", "commit": "master" }
+]