Overview browser improvement of Buses management

[ClotildeToullec]

Buses management in overview browser could be much better.

Now

There is a 'Add bus' button, identical to other browsers, with selection. We can't remove buses.

Ideas

• Remove the 'Add buses' button
• Add a '+' button to the buses list
• Show a button in each bus presenter informing about the number of browsers using this bus, opening a list popup when clicked. We could then open each browser or move it to top.
• If a bus is not used, enable a 'delete' button.

[ClotildeToullec]

The browsers menu could also be improved