logic: Added SourceGroupCustomCommand to use with SourcetrailDB binaries

* Added new Source Group type SourceGroupCustomCommand to UI and ProjectSettings
* The Source Group executes a specified command on every source file
* The variables $SOURCE_PATH, $PROJECT_PATH, $DB_PATH, $STORAGE_VERSION can be passed
* The commands are executed after all other source groups finished indexing
* The command is executed with working directory set to project directory
* Errors during command execution are shown as status update and in the Status View
* SourceGroupCustomCommand cannot be partially cleared, when one file needs clearing the project must be fully re-indexed

src/lib/data/indexer/IndexerCommandCustom.cpp

@@ -0,0 +1,46 @@
+#include "IndexerCommandCustom.h"
+
+#include <QJsonArray>
+#include <QJsonObject>
+
+IndexerCommandType IndexerCommandCustom::getStaticIndexerCommandType()
+{
+	return INDEXER_COMMAND_CUSTOM;
+}
+
+IndexerCommandCustom::IndexerCommandCustom(
+	const FilePath& sourceFilePath,
+	const std::wstring& customCommand
+)
+	: IndexerCommand(sourceFilePath)
+	, m_customCommand(customCommand)
+{
+}
+
+IndexerCommandType IndexerCommandCustom::getIndexerCommandType() const
+{
+	return getStaticIndexerCommandType();
+}
+
+size_t IndexerCommandCustom::getByteSize(size_t stringSize) const
+{
+	size_t size = IndexerCommand::getByteSize(stringSize);
+
+	return size;
+}
+
+const std::wstring& IndexerCommandCustom::getCustomCommand() const
+{
+	return m_customCommand;
+}
+
+QJsonObject IndexerCommandCustom::doSerialize() const
+{
+	QJsonObject jsonObject = IndexerCommand::doSerialize();
+
+	{
+		jsonObject["custom_command"] = QString::fromStdWString(m_customCommand);
+	}
+
+	return jsonObject;
+}