Gold linker, CCache, Stats, LGTM

- Increases linker performance under Linux builds by using Gold linker, if available
- ccache is used if available
- removed statistic class (Stats.cpp) from project due to the missing result (sorry @Brindosch)
- add LGTM bandges for code analysis overview

Signed-off-by: Paulchen-Panther <Paulchen-Panter@protonmail.com>

libsrc/webserver/QtHttpServer.h

@@ -49,7 +49,7 @@ public:
 	quint16 getServerPort    (void) const;
 	QString getErrorString   (void) const;
 
-	const bool isListening(void) { return m_sockServer->isListening(); };
+	bool isListening(void) { return m_sockServer->isListening(); };
 
 public slots:
 	void start           (quint16 port = 0);

libsrc/webserver/StaticFileServing.cpp

@@ -23,7 +23,7 @@ StaticFileServing::StaticFileServing (QObject * parent)
 
 StaticFileServing::~StaticFileServing ()
 {
-
+	delete _mimeDb;
 }
 
 void StaticFileServing::setBaseUrl(const QString& url)