Delete CaptionWordList

Refactors the Caption Class so that it does not have a CaptionWordList
property, and instead goes back to using a generic List<CaptionWord>.
In Editor Caption, this property is replaced by a generic
List<EditorCaptionWord>, and the relevant properties are either
overridden or replaced in EditorCaption.
Fix Bug HighlightCurrentWord

Fixes bug where HighlightCurrentWord would send out a NothingSelected
event when the caret moves but is still on the same word.
Add Event Handler to MarkupController

Adds an event handler for SelectedCaption.PropertyChanged.
Modify SelectedCaption_PropertyChanged

Adds a switch statement for each property.
Update CaptionTextBox On text Change