Configure external windows for browser and electron

[lucas-koehler]

The newly opened windows should only have a minimal frame showing the externalized widget. This has to be configured for electron and browser windows.
We want to remove all unneeded UI elements that extend over the minimal window/popup frame:

• Windows should still have controls to minimize, maximize, close
• Remove location/url and status bars
• Remove all window menus (especially relevant for electron)

If this results in different window opening handling for browser and electron in the WidgetExtractionHandler, the window opening code should be extracted to a new service (e.g. could be named ExternalWindowFactory) that is implemented for browser and electron. It is then injected into the WidgetExtractionHandler and used to create new windows.

In electron, this might need adaptions of window creation handling in the electron backend. Good starting points are the ElectronMainApplication and TheiaElectronWindowFactory to look into this.

[lucas-koehler]

I am looking into this.