Visual fixes & Create DebugBar class (issue #9, #8)

This version introduces multiple enhancements:

changes some methods to static
rebuild some methods
added default messages methods
updated example
added some styles

Details of additions/deletions below:
--------------------------------------------------------------

Modified:   Debug/DebugBar.php
            -- Added --
                MESSAGES
                TIME
                addInfo
                addWarning
                addError
                addSuccess
                _addMessage
                startMeasure
                stopMeasure
                measure
                _measure
            -- Updated --
                $_debugBar changed to static
                $_debugBarRenderer changed to static
                __construct, removed some unused code
                _addExtendedAssets
                renderHead changed to static
                render changed to static
                setCollector usage of static methods
                __call changed to __callStatic
            -- Removed --
                $assetsUrl

Modified:   examples/debugbar.php
            -- Updated --
                changed usage of debug bar methods to static

Modified:   Debug/Assets/dark.css
            -- Added --
                added some styles for messages