Added support for time signature on the middle & end of stave.

Similar with ClefNote.
Added TimeSigNote to insert TimeSignature between notes,
and added addEndTimeSignature function to support time signature on the end of stave.
![2014-02-21 19 40 20](https://f.cloud.github.com/assets/2025065/2228981/9b6198ba-9ae4-11e3-82dc-be309dd22a1b.png)
![2014-02-21 19 40 13](https://f.cloud.github.com/assets/2025065/2228982/9b7fcbbe-9ae4-11e3-88e2-18e5fc24b064.png)