Add support for configurably including strings

* Add json-loader to load JSON files via webpack
* Add a JSON file for string overrides
* Add a getter method to BaseString for an easier and more clearly
defined approach to accessing string values

awx/ui/client/lib/services/base-string.service.js

@@ -1,16 +1,61 @@
+import defaults from '../../assets/default.strings.json';
+
 let i18n;
 
 function BaseStringService (namespace) {
     let t = i18n._;
 
+    const ERROR_NO_NAMESPACE = t('BaseString cannot be extended without providing a namespace');
+    const ERROR_NO_STRING = t('No string exists with this name');
+
+    if (!namespace) {
+        throw new Error(ERROR_NO_NAMESPACE);
+    }
+
     this.t = t;
     this[namespace] = {};
 
+    /*
+     * These strings are globally relevant and configured to give priority to values in
+     * default.strings.json and fall back to defaults defined inline.
+     */
+    this.BRAND_NAME = defaults.BRAND_NAME || 'AWX';
+
+    /*
+     * Globally relevant strings should be defined here to avoid duplication of content across the
+     * the project.
+     */
     this.CANCEL = t('CANCEL');
     this.SAVE = t('SAVE');
     this.OK = t('OK');
-}
 
+    /**
+     * This getter searches the extending class' namespace first for a match then falls back to
+     * the more globally relevant strings defined here. Strings with with dots as delimeters are
+     * supported to give flexibility to extending classes to nest strings as necessary.
+     *
+     * If no match is found, an error is thrown to alert the developer immediately instead of
+     * failing silently.
+     */
+    this.get = name => {
+        let keys = name.split('.');
+        let value;
+
+        keys.forEach(key => {
+            if (!value) {
+                value = this[namespace][key] || this[key];
+            } else {
+                value = value[key];
+            }
+
+            if (!value) {
+                throw new Error(ERROR_NO_STRING);
+            }
+        });
+
+        return value;
+    };
+}
 
 function BaseStringServiceLoader (_i18n_) {
     i18n = _i18n_;