debian: Build-depend on libfeedback

Will be needed in the following commits.

debian/control

@@ -11,6 +11,7 @@ Build-Depends:
  libglib2.0-dev,
  libgnome-desktop-3-dev,
  libgtk-3-dev,
+ libfeedback-dev,
  librust-bitflags-1-dev (>= 1.0),
  librust-clap-2+default-dev (>= 2.32),
  librust-gio+v2-44-dev,