[5.3] MSTR-275: do not require sub module, let core handle it (#522)

If the app assets is loading from external `source_url`, if the app tries to require its
sub modules directly it will fail and the app won't load at all.

Changing the module name to its external `source_url` as what Monster UI core was
previously doing won't always work in case the sub modules were small enough and optimized
away in a single file as `app.js`. This has been observed with `branding` and
`call-recording` apps so far.

Instead we can explicitly config the paths for sub module and its external source url for
`requirejs` to load it, if it is not already optimized in the `app.js`.

Without this change, because `app.js` is requiring the submodules, this URL will be used
instead of external source_url:

```
http://{monster_ui_url}/apps/:appname/submodules/{submodule}/{submodule}.js
```

`requireSubModule` from `monster.apps.js` will require all submodules
defined on the app and can adds external `source_url` of the sub module in requirejs
config so the correct URL will be used for fetch if it is needed:

```
http://{app_metadata.source_url}/submodules/{submodule}/{submodule}.js
```

Read more: https://requirejs.org/docs/jquery.html#modulename

app.js

@@ -3,25 +3,6 @@ define(function(require) {
 		_ = require('lodash'),
 		monster = require('monster');
 
-	var appSubmodules = [
-		'callLogs',
-		'devices',
-		'featureCodes',
-		'groups',
-		'myOffice',
-		'numbers',
-		'strategy',
-		'strategyHours',
-		'strategyHolidays',
-		'users',
-		'usersCallForwarding',
-		'vmboxes'
-	];
-
-	require(_.map(appSubmodules, function(name) {
-		return './submodules/' + name + '/' + name;
-	}));
-
 	var app = {
 		name: 'voip',
 
@@ -79,7 +60,20 @@ define(function(require) {
 			disableFirstUseWalkthrough: monster.config.whitelabel.disableFirstUseWalkthrough
 		},
 
-		subModules: appSubmodules,
+		subModules: [
+			'callLogs',
+			'devices',
+			'featureCodes',
+			'groups',
+			'myOffice',
+			'numbers',
+			'strategy',
+			'strategyHours',
+			'strategyHolidays',
+			'users',
+			'usersCallForwarding',
+			'vmboxes'
+		],
 
 		render: function(container) {
 			var self = this,