Playtest fixes: windows, keys, walking, text fields, front end

The interface and input items of the first alpha playtest (user's items 6, 12, 13, 16–21), branch fix/ui-input:

• Windows keep a stable stacking order, the last one opened or clicked on top (no more crafting and backpack trading places every second); the order is in the layout file.
• I opens only the backpack (GI debug views on F7).
• A held run, an attack, a cast or any action ends a click-to-walk, online and offline.
• Backpack, bags, corpses and chests float without a dark window behind the gump.
• The front end shows no game windows and passes no keys to the game.
• Text fields: Cmd/Ctrl + C, X, V, Tab between fields, Enter submits.
• The gateway no longer closes the connection of a player on the main menu or the character screens after 20 s (only silent connections).

Done when the coordinator merges it into the alpha build and the next playtest confirms.