Rework style dialog and add bold/italic/underline/center

Also makes background color a setting independent of border,
hides style create controls until the user clicks a link,
adds a Create button to immediately create a new style,
allows non-leading numbers in style name,
and gives instructions when bad chars typed.
Merge pull request #79 from JohnThomson/moreTab

Rework style dialog and add bold/italic/underline/center