control: Get display dimensions automatically

It is no longer necessary to specify width and height in the configuration.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
images: Remove unused background image

Signed-off-by: Stefan Weil <sw@weilnetz.de>
images: Fix english text in unused background image

Signed-off-by: Stefan Weil <sw@weilnetz.de>
control: Move code for new window to new function

Signed-off-by: Stefan Weil <sw@weilnetz.de>
control: Simplify code

Open URL directly instead of using curl.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
control: Clean code and formatting

Signed-off-by: Stefan Weil <sw@weilnetz.de>