Allow keyboard navigation to edit files, improve status bar

[ll-nick]

The main contribution of this PR is the fact that it is now possible to open the "edit source file" drop down and select a file using the keyboard only ("e" to open the dropdown, j/k/arrows to navigate, enter to select).
On top of that, the "open synced window" button got a shortcut ("n" as in "new") and I made some smaller tweaks to the status bar:

• All buttons got tooltips, including a live state for the connected/disconnected indicator
• For the latter, I found a better way to visualize the current state that works well for the color blind (as opposed to the red/green dot)
• Some tooltips were misaligned or cropped, that's fixed now