S allius/issue394 (#400)

* store logging path in Config class

* rename template files and page files

* jump to referer page

- after changing the language, we jump to
  the referer page, if the attribute exists

* build and send list of log-files

* rename Download page into Log files

* initialize log-path in test config

* improve dashboard unit tests

 - add log file tests
 - check content-languages after language switch

* initialize config structure for log-file tests

* add test log file to project

* add sub_dir to test log path

- non files must be skipped. To test this we add
  a sub directory to the test log directory

* add german translations

* set quart debug flag for debug versions

* update changelog

app/tests/test_inverter_g3p.py

@@ -37,6 +37,7 @@ def config_conn():
         },
         'solarman':{'enabled': True, 'host': 'test_cloud.local', 'port': 1234}, 'inverters':{'allow_all':True}
     }
+    Config.log_path='app/tests/log/'
 
 @pytest.fixture(scope="module", autouse=True)
 def module_init():