Expose measure number and repeat list to plugins

Needed for my plugin Repeat list (http://musescore.org/fr/project/repeatlist).
It's not if you start to play with the measure offset (Measure properties -> offset) to start measure number at 1 for example. Also Score::measure is returning a measureBase... so in the indexes the frames are also counted. If you have a a title frame the idx will start at 1 for the first measure (0 being the title frame). If you have some frames for instrument names or for Coda, it will be the same...