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
Merge pull request #231 from mgavioli/Hide_some_styles_in_some_contexts

Hide some styles in some contexts