logging: Create a new level DEBUG_FILTERS

This is a cleaner approach that requires less configuration
in other applications.
This also easily allows us to have another color.

Many checks were made on being exactly at the DEBUG level, they were
fixed to also check on being below DEBUG (i.e. DEBUG_FILTERS).

weboob/tools/application/qt/qt.py

@@ -223,7 +223,7 @@ class QtDo(QObject):
         elif isinstance(error, UserError):
             if not msg:
                 msg = type(error).__name__
-        elif logging.root.level == logging.DEBUG:
+        elif logging.root.level <= logging.DEBUG:
             msg += u'<br />'
             ul_opened = False
             for line in backtrace.split('\n'):