Add window controls to the "updating cache/installing packages" dialog

[Lanchon]

Is your feature request related to a problem? Please describe.
For whatever reason, the "updating cache/installing packages" dialog is currently a second-class window:

• no maximize/restore button
• no minimize button
• does not show in taskbar

Describe the solution you'd like
I would argue that unneeded special cases are undesirable. Unless there is a technical reason for the window not to show in taskbar nor be able to minimize, i would fix that and make it behave like a more standard window.

Even if there is such a reason, then at least provide maximize/restore functions. I see no reason not to provide at least that.

Describe alternatives you've considered
N/A

Additional context
The "updating cache/installing packages" dialog showing no window controls: