Add namespaced class support for Phinx migrations

This adds support for configuring `Phinx` migrations with namespaces.
To make use of this new feature, add the following block to the
`project.ini`:

```ini
[Migration]
NamespacedPaths[Namespace\Path]=extension/mysite/migrations
```

Multiple namespaced paths can be added if needed.

Aplia/Migration/Configuration.php

@@ -80,6 +80,8 @@ public function makePhinxConfiguration() {
         $projectIni = eZINI::instance('project.ini');
         if ($projectIni->hasVariable('Migration', 'Path')) {
             $migrationsPath = $projectIni->variable('Migration', 'Path');
+        } else if ($projectIni->hasVariable('Migration', 'NamespacedPaths')) {
+            $migrationsPath = $projectIni->variable('Migration', 'NamespacedPaths');
         } else {
             $migrationsPath = "extension/site/migrations";
         }

README.md

@@ -650,6 +650,13 @@ path must be configured in `project.ini`, add the following:
 Path=extension/mysite/migrations
 ```
 
+Or if you have migrated to using namespaces, add the following (multiple namespaced paths can be added if needed):
+
+```ini
+[Migration]
+NamespacedPaths[Namespace\Path]=extension/mysite/migrations
+```
+
 Then use `vendor/bin/phinx` to handle migrations, remember to add `-c phinx.php` to
 after all commands. For instance to see the current status.