Hide some styles in some contexts

Allows to hide some styles in:
*) the Text Style editor left-side list
*) in style drop lists / combo boxes as the EditTools widget or the "Text Properties" dlg box

Currently,
*) DEFAULT style is hidden everywhere
*) FIGUREDBASS and CHORDNAME styles are hidden in the Text Style editor.

See dev-list thead http://dev-list.musescore.org/Finalizing-FiguredBass-text-styles-tp7577857.html for a discussion.