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.h

@@ -0,0 +1,29 @@
+#ifndef INDEXER_COMMAND_CUSTOM_H
+#define INDEXER_COMMAND_CUSTOM_H
+
+#include <vector>
+#include <string>
+
+#include "IndexerCommand.h"
+
+class IndexerCommandCustom
+	: public IndexerCommand
+{
+public:
+	static IndexerCommandType getStaticIndexerCommandType();
+
+	IndexerCommandCustom(const FilePath& sourceFilePath, const std::wstring& customCommand);
+
+	IndexerCommandType getIndexerCommandType() const override;
+	size_t getByteSize(size_t stringSize) const override;
+
+	const std::wstring& getCustomCommand() const;
+
+protected:
+	QJsonObject doSerialize() const override;
+
+private:
+	std::wstring m_customCommand;
+};
+
+#endif // INDEXER_COMMAND_CXXL_H