Refactor MarkupController

Removes the captionLoaded boolean as it is not being used for anything.
Add ContainedInSelection Method
Refactor Switch Statements

Adds or changes the default case for Enums to an
InvalidEnumArgumentException.
Change MarkupController.LoadCaption()

LoadCaption clears the Selected word and disables Emotion and Intensity
boxes.
Add MultipleCaptionWordsSelected Event

Adds the MultipleCaptionWordsSelected event to CaptionTextBox. Adds
Adds event handler to MarkupController. Adds documentation for several
items.
Add Markup For Multiple Selected Words

Highlighting multiple words and setting an emotion and intensity will
apply that set value to all selected words.
Update Markup For Multiple CaptionWords

Selecting multiple captions works properly, and now CaptionTextBox does
not hide its selection on focus loss.