[partition] Reduce lambda-happiness

- Make some methods that are called mostly as slots, actual slots,
   instead of going through extra lambdas.
 - Use QOverload<>::of for disambiguation instead of homebrew casts.

src/modules/partition/gui/PartitionPage.cpp

@@ -90,22 +90,9 @@ PartitionPage::PartitionPage( PartitionCoreModule* core, QWidget* parent )
 
     updateFromCurrentDevice();
 
-    connect( m_ui->deviceComboBox, &QComboBox::currentTextChanged,
-             [ this ]( const QString& /* text */ )
-    {
-        updateFromCurrentDevice();
-    } );
-    connect( m_ui->bootLoaderComboBox, static_cast<void(QComboBox::*)(const QString &)>(&QComboBox::activated),
-                [ this ]( const QString& /* text */ )
-    {
-        m_lastSelectedBootLoaderIndex = m_ui->bootLoaderComboBox->currentIndex();
-    } );
-
-    connect( m_ui->bootLoaderComboBox, &QComboBox::currentTextChanged,
-             [ this ]( const QString& /* text */ )
-    {
-        updateBootLoaderInstallPath();
-    } );
+    connect( m_ui->deviceComboBox, &QComboBox::currentTextChanged, this, &PartitionPage::updateFromCurrentDevice );
+    connect( m_ui->bootLoaderComboBox, QOverload<int>::of(&QComboBox::activated), this, &PartitionPage::updateSelectedBootLoaderIndex );
+    connect( m_ui->bootLoaderComboBox, &QComboBox::currentTextChanged, this, &PartitionPage::updateBootLoaderInstallPath );
 
     connect( m_core, &PartitionCoreModule::isDirtyChanged, m_ui->revertButton, &QWidget::setEnabled );
 
@@ -512,6 +499,12 @@ PartitionPage::updateBootLoaderInstallPath()
     m_core->setBootLoaderInstallPath( var.toString() );
 }
 
+void
+PartitionPage::updateSelectedBootLoaderIndex()
+{
+    m_lastSelectedBootLoaderIndex = m_ui->bootLoaderComboBox->currentIndex();
+}
+
 void
 PartitionPage::updateFromCurrentDevice()
 {

src/modules/partition/gui/PartitionPage.h

@@ -50,6 +50,14 @@ public:
     int selectedDeviceIndex();
     void selectDeviceByIndex( int index );
 
+private slots:
+    /// @brief Update everything when the base device changes
+    void updateFromCurrentDevice();
+    /// @brief Update when the selected device for boot loader changes
+    void updateBootLoaderInstallPath();
+    /// @brief Explicitly selected boot loader path
+    void updateSelectedBootLoaderIndex();
+
 private:
     QScopedPointer< Ui_PartitionPage > m_ui;
     PartitionCoreModule* m_core;
@@ -67,8 +75,6 @@ private:
 
     void updatePartitionToCreate( Device*, Partition* );
     void editExistingPartition( Device*, Partition* );
-    void updateBootLoaderInstallPath();
-    void updateFromCurrentDevice();
     void updateBootLoaderIndex();
 
     /**