Include transparent button style in themes

Idea created by fitch on Aug 16, 2016

    Issue: it's very common to need an icon-only button with no background fill or border, but this style is not part of the default themes.


    Idea: include a button style in the default themes that has no fill or border.


    Detail: home buttons, navigation buttons, info/help buttons, small icons in portals, etc. -- many buttons make sense with no background fill or border, i.e., the icon itself is the click target, not a box-shaped button. I end up needing to create this style in every file I create. It would save time if this style was already included in the themes.


    The current button styles are:

    Default (light), Accent Button 1-4 (colors), Navigation Button (black)


    The new style could be named Transparent or No Fill or something like that.