Rename CProgressBar numeric "caption" setting to "progress" to distinguish it from the Button, Input, Text and Tooltip "caption" setting values that are tag-formatted texts.
Remove TODO question from rP1232 since the class updates correctly.
Differential Revision: https://code.wildfiregames.com/D2419
Tested on: clang 9.0.0, Jenkins/gcc6, Jenkins/vs2015