Add support for disabling plugins (#4141)

* Move timestamp to own file
* Backend changes
* UI changes

graphql/documents/queries/plugins.graphql

@@ -2,6 +2,7 @@ query Plugins {
   plugins {
     id
     name
+    enabled
     description
     url
     version
@@ -26,6 +27,7 @@ query PluginTasks {
     plugin {
       id
       name
+      enabled
     }
   }
 }