Add an option to disable client window resizes

This goes great with tmux when you are sharing your terminal for
presentations and you don't want to give viewers the ability to resize
your terminal

app/client_context.go

@@ -197,14 +197,24 @@ func (context *clientContext) processReceive() {
 				return
 			}
 
+			rows := uint16(context.app.options.Height)
+			if rows == 0 {
+				rows = uint16(args.Rows)
+			}
+
+			columns := uint16(context.app.options.Width)
+			if columns == 0 {
+				columns = uint16(args.Columns)
+			}
+
 			window := struct {
 				row uint16
 				col uint16
 				x   uint16
 				y   uint16
 			}{
-				uint16(args.Rows),
-				uint16(args.Columns),
+				rows,
+				columns,
 				0,
 				0,
 			}