Move TUI command window code

Move TUI command window code

Like the earlier change to the data window, this moves the TUI command
window code to tui-command.[ch], and removes the old "structuring"
comments from tui-command.c.

gdb/ChangeLog
2019-07-17  Tom Tromey  <tom@tromey.com>

	* tui/tui.c: Update.
	* tui/tui-win.c (tui_cmd_window::do_make_visible_with_new_height)
	(tui_cmd_window::max_height): Move to tui-command.c.
	* tui/tui-layout.c: Update.
	* tui/tui-data.h (struct tui_cmd_window): Move to tui-command.h.
	* tui/tui-data.c (tui_cmd_window::clear_detail): Move to
	tui-command.c.
	* tui/tui-command.h (struct tui_cmd_window): Move from
	tui-data.h.
	* tui/tui-command.c: Remove "structuring" comments.
	(tui_cmd_window::clear_detail)
	(tui_cmd_window::do_make_visible_with_new_height)
	(tui_cmd_window::max_height): Move from elsewhere.