Easy to find commit on network graph

1. The commit is marked and displayed in the center.
2. Enable to display the commit older than 650th commit.
3. Add search box for the commit.

### Screenshot

![easy-to-find-commit-on-network-graph](https://f.cloud.github.com/assets/72138/126266/c3a3d820-6f47-11e2-8895-6e68887190c0.png)