Allow plugins to provide multiple buttons onto the menubar

[OItisTang]

This is the Netease Music app on macOS which has a multiple-buttons toolbar on the menubar.

I hope SwiftBar allows plugins to add buttons directly onto the menubar,
instead of only allow adding actions into menu.

[melonamin]

Technically you can make a SwiftBar plugin that will not present a menu and act like a button. The problem is that currently you can have only one menu bar item per plugin, so if you want to recreate what you have on the screenshot:

• Lyrics - one plugin
• Toolbar - one plugin for each control, 4 in total
• Main app - one plugin

So this will be 6 plugins in total, which is ugly but should work! :)
I will think about adding an ability for plugins to create more than one menubar item, but no promises