Add proof-of-concept selection support to terminal

Next will be to support mouse selections so we can copy and paste
something more interesting than just 'selection data'.
diff --git a/clients/window.h b/clients/window.h
index 9d6a22a..d67aeda 100644
--- a/clients/window.h
+++ b/clients/window.h
@@ -47,6 +47,9 @@
 struct wl_compositor *
 display_get_compositor(struct display *display);
 
+struct wl_shell *
+display_get_shell(struct display *display);
+
 #ifdef EGL_NO_DISPLAY
 EGLDisplay
 display_get_egl_display(struct display *d);
@@ -243,4 +246,10 @@
 struct wl_input_device *
 input_get_input_device(struct input *input);
 
+int
+input_offers_mime_type(struct input *input, const char *type);
+int
+input_receive_mime_type(struct input *input, const char *type);
+
+
 #endif