Textbox rendering tweaks

Speaker's name is displayed in all caps; name is drawn after dialogue to
prevent artifacts due to text "reveal" effect
More textbox rendering tweaks

Added padding on sides of box. "Last speaker" tracking removed; speaker
will always be displayed on first line of new textbox regardless of who
spoke last.
Remove Thumbs.db from repository

Also added Thumbs.db to .gitignore so such files won't sneak in again!