Update notice when new version is live

[MoltenCoffee]

Hi!
I was looking into the option to notify users when a new version is available, and add a little bit of code to do just that. It uses the GitHub API to retrieve data about releases, and compares the tag_name to the version of the running instance (via process.env.VERSION).

When a new version is available, a banner is displayed on top of pages when logged in. As I'm writing this I notice a Toast-component as well, but I don't know what's the right trade-off between the importance of updating, user-friendliness and visibility.

At the moment, although it's wrapped in useMemo, it will pretty much fetch the GitHub API on every render, which of course is a tad overkill. Storing the last time it checked for a new version, and the latest version at that moment in Local- or Sessionstorage to check once every session or day, would probably be a better option. I have never worked with Redux however, so I didn't implement it as of now.

Consider this PR more of a proof of concept as of now! Would love to hear some thoughts.

Edit: this uses v3 of the GitHub API, which is still REST. I assume this will be supported for some time, although they seem to be actively pushing to using the GraphQL version. GitHub states you should explicitely state the version in an Accept header, this is not implemented here, but it still works.

[mikecao]

I'll pull this in and make some changes later. Will probably use redux or localStorage so we don't keep checking. This should also be configurable in Settings, maybe opt-out by default. Also this should only display to the admin since other users won't have any control over the installation.