Builtin plugins (#3889)

* Allow loading of "builtin" plugins, even if "plugins" are not explicitly loaded

* Updates for 'admin' buttons:

- Make them work like proper links
- Hidden if 'hide_admin_link' customization option is set
- Check for user staff status

* Cleanup rendering of "plugins" display

* Consolidate InvenTree barcode plugins into single plugin class

* Hide "install plugin" button if plugins are not enabled

* Add info message is external plugins are not enabled

* Fixes for loading plugins

- Always load 'builtin' plugins
- Refactor calls to "is_active" at various points in codebase

* Various tweaks

- Improve builtin plugin descriptions
- Spelling fixes

* Adjust plugin detail for builtin plugins

* Simplify barcode plugin class

* Simplify template rendering

* Bug fix for inventree barcode plugin

* Revert "Simplify template rendering"

This reverts commit 3a6755a659.

* Re-re-improve template rendering

- Required as the template has been refactored for both "active" and "inactive" plugins

* Fixing unit tests for barcode plugin

* Ensure that barcode scan actions do not take a "long time":

- Add a default timeout of 0.1s to any POST or GET request in the testing framework
- Can be overridden by calling method if desired

* Display plugin "builtin" status in admin panel

* Fix unit tests for plugin API

* Further unit testing fixes

* Version number tweaks

* Further tweaks for unit testing

* Allow longer timeout for report printing via API

* Increase default timeout for API tests

- Sometimes CPU spike can cause the test to fail :|

* label printing can take a bit longer

* Remove timeout requirement from API tester

- Too variable to be reliable for CI

InvenTree/report/tests.py

@@ -305,6 +305,7 @@ class TestReportTest(ReportTest):
         InvenTreeSetting.set_setting('REPORT_ATTACH_TEST_REPORT', True, None)
 
         response = self.get(url, {'item': item.pk}, expected_code=200)
+
         headers = response.headers
         self.assertEqual(headers['Content-Type'], 'application/pdf')