Remove external pending call reference when reply message is received

Used to just clear the pointer, which created a memory leak.
Unify whitespace
Remove evdev I/O watches on mce exit

Makes valgrind output less noisy.
Release setting change signal cache on mce exit

Makes valgrind output less noisy.
Remove main D-Bus signal filter on mce exit

Makes valgrind output less noisy.
Cleanup signal transfer pipe on mce exit

Makes valgrind output less noisy.
Do not use blocking dbus queries for enumerating active voice calls

The dbus_send_with_block() helper must not be used anymore.

Handle query asynchronously.