Add loading spinner to pod management page

[minimalparts]

When making a query from the pod management page, the PeARS install will first update its database with the latest info from the GitHub repo (it is set to do this if current local files are older than an day). This takes a moment, while the new files are downloaded. But nothing tells the user about this, and if their internet connection is a little slow, they might think the program is hanging. So we should add a loading spinner or equivalent to provide feedback.