Ability to display more notes more compactly

Our users want to be able to see more notes at once (andulv/RSTabExplorer#7) but when use the scale setting everything quickly becomes more difficult to read.

Setting beatsPerBar to 4 isn't suitable: having a bar with 20 notes squashed into a small space doesn't work, and having 12 empty bars take a whole page is wasteful. Also it causes some buggy rendering.

Instead I wanted to be able to keep the automatic layout while having the option to reduce how far apart notes are.

I've got it working by adding a setting which scales the width of GlyphBeatBase.

![screenshot-p146](https://cloud.githubusercontent.com/assets/1028741/2897092/87ff10b2-d578-11e3-957c-e1e57c95ed65.png)