Use atomics for config chain. Closes T596
Use atomics for config chain. Closes T596

Summary:
This Ansatz basically replaces the old non-atomic pointers with atomic pointers and
optimizes poll_config by adding a new non-atomic pointer to be used only by this function.

Doing away with the linked list completely by using the atomic interface of shared_ptr was
unfortunately not possible as they were not lock-free on several test machines.

I additionally renamed some variables to better highlight the list-like data structure.

Test Plan: Manually review code, Use debugger to verify correct loading and cleanup

Reviewers: tobias

Reviewed By: tobias

Maniphest Tasks: T596

Differential Revision: https://dev.openmha.org/D290

HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA