Change color of untracked/changed file?

[Kyohei Uto]

I'm implementing the feature as title says:

A few notes:

• The color is now fixed to Red(1), but it may be better to make it changable in config file.
• At the first place this may be noisy, so adding e.g. untraced_file to config to opt out might be a good idea.

[Kyohei Uto]

Merged to develop by f614d7c

[Kyohei Uto]

Released in v2.9.0