feat: add ConcurrentTask

This tasks (or rather, meta-task) has the ability to run several other
sub tasks concurrently.

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/CMakeLists.txt

@@ -418,6 +418,8 @@ set(TASKS_SOURCES
     # Tasks
     tasks/Task.h
     tasks/Task.cpp
+    tasks/ConcurrentTask.h
+    tasks/ConcurrentTask.cpp
     tasks/SequentialTask.h
     tasks/SequentialTask.cpp
 )