Gang-rework bugfixes and rebalancing. Started adding Gang API

src/NetscriptGang.js

@@ -0,0 +1,17 @@
+import {Player}                 from "./Player";
+import {Gang}                   from "./Gang";
+import {makeRuntimeRejectMsg}   from "./NetscriptEvaluator";
+
+function unknownGangApiExceptionMessage(functionName, err) {
+	return `gang.${functionName}() failed with exception: ` + err;
+}
+
+function checkGangApiAccess(workerScript, functionName) {
+	const accessDenied = `gang.${functionName}() failed because you do not currently have a Gang`;
+	const hasAccess = Player.gang instanceof Gang;
+	if (!hasAccess) {
+		throw makeRuntimeRejectMsg(workerScript, accessDenied);
+	}
+}
+
+export {unknownBladeburnerActionErrorMessage, unknownBladeburnerExceptionMessage, checkBladeburnerAccess};