[refactor] Breaking out key codes

Trying to start breaking apart the large circular dependencies between
modules. Most of the dependencies are similar to this pattern where
there is one stand-alone member that is needed, so the entire module
gets brought along with.

src/engine.js

@@ -63,7 +63,8 @@ import {StockMarket, StockSymbols,
         initSymbolToStockMap, stockMarketCycle,
         updateStockPrices,
         displayStockMarketContent}              from "./StockMarket";
-import {Terminal, postNetburnerText, post, KEY} from "./Terminal";
+import {Terminal, postNetburnerText}            from "./Terminal";
+import {KEY}                                    from "../utils/helpers/keyCodes";
 
 // These should really be imported with the module that is presenting that UI, but because they very much depend on the
 // cascade order, we'll pull them all in here.