updated documentation

Change-Id: I710dd1df715c58b6383ae06dc737eac462d11de6
CustomLayerWindow no longer uses hard-coded list of plotters.
Renamed AutoResizingTextArea -> Paragraph, set more common defaults, and
improved whitespace trimming behavior.
AlertTextBox now selects all text when it opens.
Added help text to SessionStateEditor's linking controls.
Code & GUI cleanup.

Change-Id: I9f30a3a48bd589b74242423b187afa508439aed0