Change classname for playbutton in app.js
Change font-family-variable for iconfont to 'podlove'
new big playbutton

Remove bigplay mixin and leave only rules in _titlebar.scss
that deal with flexbox-layout.
Instead, put all styles in class *play* in _buttons.scss and
create variables for $play-button-size and ~margin.
Merge pull request #190 from podlove/new-playbutton-icon

Apply new iconfont on playbutton