appDisplay: Reimplement well layout to be width-independent

Use ShellGenericContainer to implement a fully dynamic layout
for the application well.  It's still fixed to 4 columns by default,
but no longer requires a fixed width to be passed in on start.

With another chunk of work, it could likely try to adjust to
the case where we can only fit fewer than 4 items in the well.

Remove the border highlighting on mouseover, since that caused
reallocations, and the grid layout isn't trivial.

Delete the unused shell_global_get_word_with function.

src/shell-global.h

@@ -73,8 +73,6 @@ void shell_global_format_time_relative_pretty (ShellGlobal *global, guint delta,
 
 ClutterActor *shell_global_create_root_pixmap_actor (ShellGlobal *global);
 
-guint shell_global_get_max_word_width (ShellGlobal *global, ClutterActor *ref, const char *text, const char *font);
-
 G_END_DECLS
 
 #endif /* __SHELL_GLOBAL_H__ */