Move logging defines to QMAKE instead of logging.h

Defines done outside of easylogging++.h does not work according to
official documentation
(https://github.com/zuhd-org/easyloggingpp/blob/master/README.md#configuration-macros)

"NOTE: All the macros can be defined in one of the following ways:

1. Define macros using -D option of compiler, for example in case of
g++ you will do g++ source.cpp ... -DELPP_SYSLOG -DELPP_THREAD_SAFE
... (recommended way)

2. Define macros inside "easylogging++.h" (defining macros in other
files won't work)"

Linking to this issue:
https://github.com/zuhd-org/easyloggingpp/issues/590#issuecomment-346753951

We are using the developer recommended way of defining them by command
line.

What is assumed to be the intention of enabling debug logs before
including easylogging++ never actually did anything, hence this define
is dropped. Newer versions of easylogging++ uses the macro
ELPP_DISABLE_DEBUG_LOGS to _disable_ debug logs. Leaving that macro
undefined satisfies the original intent.

src/logging.h

@@ -1,16 +1,4 @@
 #pragma once
 
 // easylogging includes
-#ifndef _DEBUG
-#    define _DEBUG
-#    define ELPP_THREAD_SAFE
-#    define ELPP_QT_LOGGING
-#    define ELPP_NO_DEFAULT_LOG_FILE
-#    include <easylogging++.h>
-#    undef _DEBUG
-#else
-#    define ELPP_THREAD_SAFE
-#    define ELPP_QT_LOGGING
-#    define ELPP_NO_DEFAULT_LOG_FILE
-#    include <easylogging++.h>
-#endif
+#include <easylogging++.h>