Add timestamps-of-interest drmemtrace scheduler feature

[derekbruening]

The drmemtrace scheduler has a regions-of-interest feature to specify subsets of a trace via instruction ordinal ranges. However, for a many-threaded trace, if these subsets should cut across all threads that were active at the same time during traces, computing the instruction ordinals for each thread requires a separate pass over every thread's trace. A simpler interface would be to provide a single timestamp range for the whole workload and have the scheduler use the recorded schedule file to map that to per-thread instruction ordinals.