Restructure "src/" folder

Moving files from the "src/" folder into "src/legacy", "src/macro-core",
and "src/utils" was necessary as it was becoming a bit too cluttered.

src/utils/file-selection.cpp

@@ -0,0 +1,49 @@
+#include "file-selection.hpp"
+
+#include <obs-module.h>
+#include <QLayout>
+#include <QFileDialog>
+
+FileSelection::FileSelection(FileSelection::Type type, QWidget *parent)
+	: QWidget(parent), _type(type)
+{
+	_filePath = new QLineEdit();
+	_browseButton =
+		new QPushButton(obs_module_text("AdvSceneSwitcher.browse"));
+
+	QWidget::connect(_filePath, SIGNAL(editingFinished()), this,
+			 SLOT(PathChange()));
+	QWidget::connect(_browseButton, SIGNAL(clicked()), this,
+			 SLOT(BrowseButtonClicked()));
+	QHBoxLayout *layout = new QHBoxLayout;
+	layout->addWidget(_filePath);
+	layout->addWidget(_browseButton);
+	layout->setContentsMargins(0, 0, 0, 0);
+	setLayout(layout);
+}
+
+void FileSelection::SetPath(const QString &path)
+{
+	_filePath->setText(path);
+}
+
+void FileSelection::BrowseButtonClicked()
+{
+	QString path;
+	if (_type == FileSelection::Type::WRITE) {
+		path = QFileDialog::getSaveFileName(this);
+	} else {
+		path = QFileDialog::getOpenFileName(this);
+	}
+	if (path.isEmpty()) {
+		return;
+	}
+
+	_filePath->setText(path);
+	emit PathChanged(path);
+}
+
+void FileSelection::PathChange()
+{
+	emit PathChanged(_filePath->text());
+}