Desktop app: do not fullscreen windows

[despens]

When starting a capturing session, the desktop app opens a full screen window every time. Depending on the user's display parameters that might be undesirable—for instance on my 27" display it creates an enormous window covering everything :wink:

All operating systems offer enough ways to manage windows, so users should be able to switch to fullscreen if they like, and the desktop app should ideally remember users' preferred window size.

The full screen button right next to the "back" navigation button has also thrown me off a few times when accidentally hitting it. I'd like to advocate to remove this button from the app.