Debug messages shall not depend on Tracer filter in UMBRELLO_LOG_TO_CONSOLE mode:

Commit 92232257 implemented this on the uml.h logDebug[0..5] macros.
Here, the same change is applied on the DEBUG() and DEBUG_N() streams.

umbrello/debug/debug_utils.h
- In class Tracer,
  - add static bool s_logToConsole;
  - add member function logToConsole() returning s_logToConsole.
- In macro DEBUG_N bypass Tracer filter if logToConsole() returns true.

umbrello/debug/debug_utils.cpp
- In static function Tracer::instance(), if s_instance is null then
  - rerieve env variable UMBRELLO_LOG_TO_CONSOLE to local QString
    umbrello_logToConsole;
  - set s_logToConsole true if umbrello_logToConsole is set to "1".

umbrello/uml.h
- Remove member m_logToConsole, it is superseded by Tracer::s_logToConsole.

umbrello/uml.cpp
- In constructor revert addition made in commit fa13dffa; env variable
  UMBRELLO_LOG_TO_CONSOLE is now interrogated by Tracer::instance().
- Update function logToConsole() to use Tracer::logToConsole().