UI|Client: Popup nesting level affects appearance

Deeply nested popups should be opaque to avoid visual clutter.
Refactor|UI|Client: Added widget for settings profile manipulation

The ProfilePickerWidget takes any SettingsRegister and allows switching
and manipulating the profiles in the register.

Used the new widget in the Renderer Settings dialog.
UI|Client|Renderer Appearance: Regrouped some settings, use profile picker

Revised the Renderer Appearance based on feedback. Profiles can be
switched now also inside the editor.

Added a "Camera Lens" group for vignette and flares/halos. Renamed
the "Textures" group to "Materials".

The extra gear button for opening Renderer Settings is gone.
Cleanup: Server build warning; Video Settings mode label