Introduce Styles class that handles the builtin styles
Use new Styles class to setup actions for builtin styles
Add possibility to choose from reveal.js built-in presentation styles
Merge branch 'wip/custom-styles' of https://github.com/cloose/CuteMarkEd into wip/custom-styles
Merge branch 'wip/custom-styles' of https://github.com/cloose/CuteMarkEd into wip/custom-styles
Fix compile with changed Style struct