Revert file-re-naming (#23)

## *What has changed?*:

## *Why was it needed?*:

## *How was it done?*:

## Links to trello Tickets or github issues: 

* 

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### Code Checklist
- [ ] tested
- [ ] documented

inc/label-printing/namespace.php

@@ -16,7 +16,7 @@
 use function is_network_admin;
 use function is_user_admin;
 
-const BASENAME   = 'label-printing/label-printing.php';
+const BASENAME   = 'label-printing/plugin.php';
 const PLUGINPATH = '/figuren-theater/' . BASENAME;
 // const PLUGINPATH = '/wpackagist-plugin/' . BASENAME; // Not yet, see #6.