refactor: Use composition for update time

The timer is not required by all classes and the deep inheritance makes
it hard to see where it is actually used. Use composition instead.

src/misc/CMakeLists.txt

@@ -319,6 +319,8 @@ add_library(misc SHARED
         swiftdirectories.cpp
         swiftdirectories.h
         swiftmiscexport.h
+        threadedtimer.cpp
+        threadedtimer.h
         threadutils.cpp
         threadutils.h
         timestampbased.cpp