Updated SignalTiming object hierarchy to add another intermediate object (SignalTimingEntry), so that SignalTimingElement could be used as the "leaf" object and track the ID of the database row (in SIGNAL_TIMINGS table) for each phase (rather than tracking phases as "content" of the SignalTimingElement).
 Changes to be committed:
	modified:   SignalTiming.java
	modified:   SignalTimingElement.java
	new file:   SignalTimingEntry.java
	modified:   ../../../../../../resources/scenario.xsd
Add createSignalTimingEntry() to ModelObjectsFactory.java
There should be no id field in SignalTiming -- it doesn't represent a row in a table.

 Changes to be committed:
	modified:   src/main/java/edu/berkeley/path/model_objects/scenario/SignalTiming.java
	modified:   src/main/resources/scenario.xsd