Merge Controller and View structs into one Application struct.

The `View` sturct was mostly a layer of indirection, and the controller benefitted by absorbing the gtk::Application
subclass parts, so now those two are merged into a new gtk::Application subclass.

src/view/port.rs

@@ -7,7 +7,7 @@ use gtk::{
 use log::warn;
 use pipewire::spa::Direction;
 
-use crate::controller::MediaType;
+use crate::application::MediaType;
 
 mod imp {
     use once_cell::{sync::Lazy, unsync::OnceCell};