Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/prompts/dist/elements/index.js

@@ -0,0 +1,13 @@
+'use strict';
+
+module.exports = {
+  TextPrompt: require('./text'),
+  SelectPrompt: require('./select'),
+  TogglePrompt: require('./toggle'),
+  DatePrompt: require('./date'),
+  NumberPrompt: require('./number'),
+  MultiselectPrompt: require('./multiselect'),
+  AutocompletePrompt: require('./autocomplete'),
+  AutocompleteMultiselectPrompt: require('./autocompleteMultiselect'),
+  ConfirmPrompt: require('./confirm')
+};