Structure for safer OpenMP
Added linked_array structure that represents linked list with subarray of constant size. This elemenates possible crash with openmp when mesh is simultaneously modified and data is accessed. Previously when array of links was reallocated in chunk_array due to mesh growth, the pointer may be simultaneously changed due to reallocation and be accessed by another thread. Now reallocation adds another segment of the array in linked list making previous records intact. To restore previous behavior undefine NEW_CHUNKS in container.hpp.