Use std::vector in NbnxnPairlistCpu

Use std::vector in NbnxnPairlistCpu

All pointers in NbnxnPairlistCpu have been replaced by std::vector.
This change is only refactoring. The only, local, functionality change
is that during list creation and entry is added to the later and later
removed when empty instead of operating on an entry that is located
one beyond the list size.

Change-Id: I984e879d1f2fa52d74aafc5c4da09c7eefbb99fb