[partition] Add setting for requiredstorage

- If the welcome module isn't used, can set a required amount
   of storage for the installation here.

src/modules/partition/gui/PartitionViewStep.cpp

@@ -69,6 +69,7 @@ PartitionViewStep::PartitionViewStep( QObject* parent )
     , m_widget( new QStackedWidget() )
     , m_choicePage( nullptr )
     , m_manualPartitionPage( nullptr )
+    , m_requiredStorageGiB( 0.0 )
 {
     m_widget->setContentsMargins( 0, 0, 0, 0 );
 
@@ -564,6 +565,9 @@ PartitionViewStep::setConfigurationMap( const QVariantMap& configurationMap )
 
     m_swapChoices = choices;
 
+    // Settings that overlap with the Welcome module
+    m_requiredStorageGiB = CalamaresUtils::getDouble( configurationMap, "requiredStorage", -1.0 );
+
     // These gs settings seem to be unused (in upstream Calamares) outside of
     // the partition module itself.
     gs->insert( "ensureSuspendToDisk", ensureSuspendToDisk );