Use new versioning api in client

The new updating scheme does the following:

1. Sends a request to `/api/v1/version/ok`
2. Gets back JSON. One of the fields is `'current_version'`. Use this to check if the client version is not equal to the current_version.
3. If not equal, use the `current_download_link` to grab the zip (most likely from Github Releases). Write the binary to `'ok'` as before.

@moowiz @Some3141 Can you take a look? The endpoint isn't working yet so I haven't been able to test it.