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_cxx/project/SourceGroupCxxEmpty.cpp

@@ -9,7 +9,6 @@
 #include "SourceGroupSettingsWithCStandard.h"
 #include "FileManager.h"
 #include "utility.h"
-#include "utilitySourceGroupCxx.h"
 
 SourceGroupCxxEmpty::SourceGroupCxxEmpty(std::shared_ptr<SourceGroupSettingsCxx> settings)
 	: m_settings(settings)
@@ -33,7 +32,7 @@ std::set<FilePath> SourceGroupCxxEmpty::filterToContainedFilePaths(const std::se
 		excludeFilters = settings->getExcludeFiltersExpandedAndAbsolute();
 	}
 
-	return utility::filterToContainedFilePaths(
+	return SourceGroup::filterToContainedFilePaths(
 		filePaths,
 		std::set<FilePath>(),
 		utility::toSet(indexedPaths),