[libcalamaresui] Refactor Requirements-Checking

- Move the actual checking into a separate object with some lifecycle-
   management signals.
 - Right now this is still single-threaded and blocking, so no net gain.

src/libcalamaresui/modulesystem/RequirementsChecker.cpp

@@ -0,0 +1,73 @@
+/* === This file is part of Calamares - <http://github.com/calamares> ===
+ *
+ *   Copyright 2019, Adriaan de Groot <groot@kde.org>
+ *
+ *   Calamares is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   Calamares is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with Calamares. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "RequirementsChecker.h"
+
+#include "Module.h"
+#include "Requirement.h"
+
+#include "utils/Logger.h"
+
+#include <QTimer>
+
+namespace Calamares
+{
+
+RequirementsChecker::RequirementsChecker( QVector< Module* > modules, QObject* parent )
+    : QObject( parent )
+    , m_modules( std::move( modules ) )
+{
+}
+
+RequirementsChecker::~RequirementsChecker()
+{
+}
+
+void
+RequirementsChecker::run()
+{
+    bool acceptable = true;
+
+    for (const auto& module : m_modules )
+    {
+        RequirementsList l = module->checkRequirements();
+        if ( l.length() > 0 )
+        {
+            cDebug() << "  .." << module->name() << "has" << l.length() << "requirements";
+            emit requirementsResult( l );
+        }
+
+        int count = 0;
+        for (const auto& r : l)
+        {
+            if ( r.mandatory && !r.satisfied )
+            {
+                cDebug() << "  .. requirement" << count << r.name << "is not satisfied.";
+                acceptable = false;
+            }
+            ++count;
+        }
+    }
+
+    emit requirementsComplete( acceptable );
+
+    QTimer::singleShot(0, this, &RequirementsChecker::done );
+}
+
+
+}