move stylesheet to skin folder (style.css)

added new datatype TimeBase128 for a better understaning of values and methods

fixed editor slider for full height, offset by half its width (centering)
moving only along the x axis

added functionality for drawing notes onto tracks (needs testing)

added methods to retrieve the song's length (in multiples of 128th notes)

added methods to jump to any given time within the song and start the playback there

fixed some minor warnings (signed/unsigned)

minor layout changes (sequencer)

adding new tracks / deleting old tracks now possible
(move SequencerTrack to the heap? change to pointer storage?)