plugin install progress (#614)

* Frontend progress bars

* Backend bit

* closure is stale i think so no closure for you

* Fix formatting of the progress svgs

* Reset progress bar when new plugin starts downloading

backend/locales/en-US.json

@@ -231,6 +231,15 @@
         "store_testing_warning": {
             "desc": "You can use this store channel to test bleeding-edge plugin versions. Be sure to leave feedback on GitHub so the plugin can be updated for all users.",
             "label": "Welcome to the Testing Store Channel"
+        },
+        "download_progress_info": {
+            "start": "Initializing",
+            "open_zip": "Opening zip file",
+            "download_zip": "Downloading plugin",
+            "increment_count": "Incrementing download count",
+            "parse_zip": "Parsing zip file",
+            "uninstalling_previous": "Uninstalling previous copy",
+            "installing_plugin": "Installing plugin"
         }
     },
     "StoreSelect": {