Utils/Console: Fix singleton instantiation order (ServerManager / Scheduler)

Scheduler: Add automatic periodic resync to ClockService::abstime() and ClockService::clock()
Scheduler: Add task nameing
Scheduler: BUGFIX: Add missing task-dequeue in FdDispatcher::add()
Scheduler: Add empty() member to all dispatchers
Scheduler: Add eventTime() support to FdManager
Scheduler: Add support for non-pollable file descriptor detection to FdManager and FdDispatcher
Scheduler: Add FIFORunner task watchdog
Scheduler: Add debugging backtrace to FIFORunner
Scheduler: Change senf::Scheduler implementation to use the new dispatcher infrastructure
Scheduler: BUGFIX: Fix access to (possibly) destroyed object in TimerEvent::run()
Utils: Add senf::signalName() helper
Utils/Daemon: Use senf::signalName() in debug messages
Utils/Logger: Fix logger to correctly format the timestamp (the deadlock should be fixed now)
Update scheduler callback signatures to the new API throughout the project
Update documentation