Move view {x,y,width,height} into container struct

This renames/moves the following properties:

* sway_view.{x,y,width,height} ->
sway_container.content_{x,y,width,height}
    * This is required to support placeholder containers as they don't
    have a view.
* sway_container_state.view_{x,y,width,height} ->
sway_container_state.content_{x,y,width,height}
    * To remain consistent with the above.
* sway_container_state.con_{x,y,width,height} ->
sway_container_state.{x,y,width,height}
    * The con prefix was there to give it contrast from the view
    properties, and is no longer useful.

The function container_set_geometry_from_floating_view has also been
renamed to container_set_geometry_from_content.

sway/commands/border.c

@@ -93,7 +93,7 @@ struct cmd_results *cmd_border(int argc, char **argv) {
 	}
 
 	if (container_is_floating(container)) {
-		container_set_geometry_from_floating_view(container);
+		container_set_geometry_from_content(container);
 	}
 
 	arrange_container(container);