perf: Fix all clazy qstring-allocation warnings (#903)

src/lib_gui/qt/element/button/QtHelpButton.cpp

@@ -16,9 +16,9 @@ QtHelpButton::QtHelpButton(const QString& helpTitle, const QString& helpText, QW
 	setAttribute(Qt::WA_LayoutUsesWidgetRect);	  // fixes layouting on Mac
 	setMouseTracking(true);
 
-	setToolTip("help");
+	setToolTip(QStringLiteral("help"));
 	setIconSize(QSize(16, 16));
-	setObjectName("helpButton");
+	setObjectName(QStringLiteral("helpButton"));
 
 	leaveEvent(nullptr);
 
@@ -28,7 +28,7 @@ QtHelpButton::QtHelpButton(const QString& helpTitle, const QString& helpText, QW
 void QtHelpButton::handleHelpPress()
 {
 	QMessageBox msgBox;
-	msgBox.setWindowTitle("Sourcetrail");
+	msgBox.setWindowTitle(QStringLiteral("Sourcetrail"));
 	msgBox.setIcon(QMessageBox::Information);
 	msgBox.setText("<b>" + m_helpTitle + "</b>");
 	msgBox.setInformativeText(m_helpText);

src/lib_gui/qt/element/button/QtHoverButton.cpp

@@ -1,6 +1,6 @@
 #include "QtHoverButton.h"
 
-QtHoverButton::QtHoverButton(QWidget* parent): QPushButton("", parent)
+QtHoverButton::QtHoverButton(QWidget* parent): QPushButton(QLatin1String(""), parent)
 {
 	setAttribute(Qt::WA_LayoutUsesWidgetRect);	  // fixes layouting on Mac
 	setMouseTracking(true);

src/lib_gui/qt/element/button/QtIconButton.cpp

@@ -5,7 +5,7 @@
 #include "utilityQt.h"
 
 QtIconButton::QtIconButton(const FilePath& iconPath, const FilePath& hoveredIconPath, QWidget* parent)
-	: QPushButton("", parent)
+	: QPushButton(QLatin1String(""), parent)
 	, m_iconPath(iconPath)
 	, m_hoveredIconPath(hoveredIconPath)
 	, m_color(Qt::transparent)

src/lib_gui/qt/element/button/QtIconStateButton.cpp

@@ -4,13 +4,13 @@
 
 #include "utilityQt.h"
 
-QtIconStateButton::QtIconStateButton(QWidget* parent): QPushButton("", parent)
+QtIconStateButton::QtIconStateButton(QWidget* parent): QPushButton(QLatin1String(""), parent)
 {
 	setSizePolicy(QSizePolicy::Fixed, QSizePolicy::Fixed);
 	setAttribute(Qt::WA_LayoutUsesWidgetRect);	  // fixes layouting on Mac
 	setMouseTracking(true);
 
-	setObjectName("iconStateButton");
+	setObjectName(QStringLiteral("iconStateButton"));
 
 	leaveEvent(nullptr);
 }