#17 track arm/disarm convenience patch

[David Yip]

When dealing with projects that have a large
number of tracks it can be tedious to ensure that
all tracks that should be not be modified in an
edit are disarmed, and vice versa. This patch
adds two small features that disarm and arm all
tracks in the project.

This patch was made against the August 1,
2002 backups.

[David Yip]