logic: allow the user to discard an aborted indexer run

* keep old database on filesystem while indexing
* migrate old ".coatiproject" settings to new ".srctrlprj" extension when loading project
* send new errors in MessageErrorCountUpdate after injecting
* recheck filepath exist() in FileSystem's remove, rename, copy and create functions
* updated tasks to new "override" policy

src/lib/utility/scheduling/TaskGroupSelector.cpp

@@ -4,10 +4,6 @@ TaskGroupSelector::TaskGroupSelector()
 {
 }
 
-TaskGroupSelector::~TaskGroupSelector()
-{
-}
-
 void TaskGroupSelector::addTask(std::shared_ptr<Task> task)
 {
 	m_taskRunners.push_back(std::make_shared<TaskRunner>(task));