Implement colorExtended in Quickmamba

This will be used to manage the colorPicker with a QColor
replace alpha() by alphaF() because we give values between 0 and 1
implement getter and setter for brightness and saturation
changed some fonctions for manage colors
New Class ColorExtended to manage colorPicker in QML
Merge branch 'master' of github.com:buttleofx/QuickMamba