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This patch refers to the settings update on closing the settings
window.

This patch is related to the endpoint URLs needed to make various
UI operations i.e., login and vising the pithos page on a browser.

The helper used to provide the GUI with all URLs necessary, while
now they are retrieved by the GUI itself, with the tokenless
request "POST <auth_url endpoint>/tokens".

Settings are loaded and updated in protocol.py
If the client is not ready yet, some GUI options are not gray
and unclickable until the client is ready.

When an upload fails, because a new upstream version exists, mark the
serial as failed, so as to skip it later.