Introduced logging in case of plugin load error

Created by: stefanoborini

Small PR that introduces basic logging in case of error at loading. Unfortunately it's not possible to retrieve the traceback, but the exception message and the exception should be a good hint.

force_bdss/tests/test_bdss_application.py

@@ -41,4 +41,3 @@ class TestBDSSApplication(unittest.TestCase):
         _import_extensions(plugins, ext)
 
         self.assertEqual(plugins[0], plugin)
-