Refactor: migrate "MessageGID" fields to class IPMessage
1. overwrite log files
2. time logs (issue time, eventual time, and ack time); leave causal
time unimplemented
Adding deps into workload generator, IPMessage, and FrontEnd
Adding deps into workload generator, IPMessage, and FrontEnd
IPMessage: "deps" of MessageGID

For each message (MessageGid): eventual time, #deps; dep1 time,  #deps;
...; causal time, #deps

TimeLogger: a collection of logger methods for recording issue time,
eventual time, deps time, causal time, and ack time

Delete deps once some message is executed.
log4j.properties: log4j.logger.util.log4j = INFO, time
UI for workload paramters: total number of requests, rate, and write
ratio.
refactor of "MessageGid" fields into super class IPMessage: Remove the
fields "qmid" and "umid" in subclasses of IPMessages:
QueryMessage, UpdateMessage, QueryAckMessage, UpdateAckMessage