Do a version check on login, to say whether the current version of jerboa supports your server.

[dessalines]

IE have a popup error that says ("Version of lemmy unsupported by X instance. Ask your server administrators to upgrade lemmy.")

This is necessary, since logging into pre 0.18 versions will fail, due to breaking API changes.

[beatgammit]

Is there a mechanism for admins to be notified of an API breakage? What about instances to auto-block other instances when API versions are incompatible?

[sockenklaus]

Isn't this a duplicate of #673?

[twizmwazin]

Duplicate of #673