MenuBar improvements

[simonhamp]

Currently, MenuBar windows are limited in what they're capable of:

• Some settings can't be changed once they've been created, such as the icon.
• The window itself doesn't have the same controls as other windows (e.g. they are always user-resizable and can't be made a fixed size).
• Some features aren't exposed, such as tooltip text.
• The window doesn't receive any events from Electron or Laravel, making it impossible to use our Native events in JS or Livewire.
• Context menus or MenuBar windows are the only option, there's no support for custom logic.

This PR aims to fix all of these issues. It also defaults to preloading the window (when there is one) so that it is visible much sooner after the user clicks on the icon, making for a much better UX.

[SRWieZ]

Awesome! Excited to try white this new PR 😃