ProtocolSelector.locateNextString: Return null if no keys
ProtocolSelector.locateNextString: Use the parameter, not the field
Document ProtocolSelector.locateNextString
ProtocolSelector: Document canonicalizeIndexing and add todo
Add renderSlides to interface SlideList

This will be used to let the ProtocolSelector automatically render
slides to a certain size.
Add PS.renderAllToSize
PS: Add renderAllToSize for maps
PS: Add a Javadoc note about modification of data
PS: Render all SlideLists to size when adding slides
Change return type of PS.renderAllToSize Map->LinkedHashMap

This is so that results can be directly stored in PS.slides.
Add PS.setSize()
Make PS.setSize set currentIndex = 0

Rendering can change the ordering of slides, so we return to the
beginning as a safeguard.
Make the D_SLs only initialize date if they haven't already

This means that the date won't be overwritten if the SlideList is, say,
read from serialization. (Not sure how serialization initializes read
objects; will need to do some reading on it, but I'm guessing that it
calls the constructor.)