Add a button to hide the synchronisation panel

[laurent22]

It should be a button with a down arrow. Clicking on it hides the panel, then the button becomes an "up" arrow. Clicking on it again, will show the panel.

It should be hidden by default.

[personalizedrefrigerator]

This seems to be related to section 2.2.2 of the Web Content Accessibility Guidelines (see #10795):

Moving, blinking, scrolling
For any moving, blinking or scrolling information that (1) starts automatically, (2) lasts more than five seconds, and (3) is presented in parallel with other content, there is a mechanism for the user to pause, stop, or hide it unless the movement, blinking, or scrolling is part of an activity where it is essential; and

Currently, it is possible to hide the entire sidebar, however, this also hides the notebook and tag lists.

[mrjo118]

Is the propsoal here that only the summary of items synced is collapsible? Frankly the sync button itself and the timestamp of the last successful sync is very useful for quick access, and it would decrease usability if they were collapsed by default

[laurent22]

Yes maybe we should only hide the debugging information and leave timestamp and button.