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/storage/sqlite/SqliteIndexStorage.cpp

@@ -44,6 +44,11 @@ namespace
 	}
 }
 
+size_t SqliteIndexStorage::getStorageVersion()
+{
+	return s_storageVersion;
+}
+
 SqliteIndexStorage::SqliteIndexStorage(const FilePath& dbFilePath)
 	: SqliteStorage(dbFilePath.getCanonical())
 {