Rename client.js to slave.js

Rename the client.js script to slave.js, and changed places where it's
refered to as client into slave.

lib/manager/modManager.js

@@ -36,7 +36,7 @@ function formatBytes(size, decimals) {
 
 /**
 Lists mods for an instance as a table. Warning, handles printing internally.
-@param {Instance} instance - Instance object, see client.js
+@param {Instance} instance - Instance object, see slave.js
 
 @example
 var modManager = require("modManager");