fix(viz): various fixes in the transfer function and image code

Description

• move the PACS configuration in a module so that it can be used in other apps
• the image is now an input and not an inout in the module::ui::qt::image::window_level service
• adjust the range of module::ui::qt::image::window_level depending on the image range
• remove the static label in the color widget of module::ui::qt::settings
• sight::data::helper::medical_image::get_min_max() now returns its values as a pair to avoid a wrong initialisation in the caller code. This is a breaking change in the API
• fix mixed rendering with binary transparent objects

How to test it?

To be tested with dependent merge-requests. Non regressions should be covered by unit-tests.