added SliderCallback class for sliders that can trigger callbacks onMouseDown
add ability to set custom fonts for a UIController
Merge pull request #6 from nselikoff/customize-fonts

add ability to set custom fonts for a UIController
Merge pull request #5 from nselikoff/slidercallback

added SliderCallback class for sliders that can trigger callbacks onMouseDown
Merge branch 'master' into resetToDefault
Merge branch 'resetToDefault' of https://github.com/nselikoff/Cinder-MinimalUI into resetToDefault
incorporate reset to default into SliderCallback class