Compute scheduler overhead for each job

[santhnm2]

List of significant changes:

• Route all GavelIterator logging through a single file per worker / job / round
• Format GavelIterator logs as a timeline, where each line is of the form [TIMESTAMP] [EVENT] [STATUS] MESSAGE
• Add code in scheduler.py to save job timelines to files
• Fix bug where latest job timestamp was being updated every round even when job was granted lease extensions
• Re-dispatch jobs with extended leases if they finish early
• Break out of scheduling loop in final round
• Add sweep script for generating timelines which can be used to measure overhead
• Add script for parsing timelines to compute overhead
• Miscellaneous bug fixes for application code