Fixes #2096. Non-free Duality.ttf removed. Open/free SpicyRice.ttf added.

Fixes #2096. Non-free Duality.ttf removed. Open/free SpicyRice.ttf added.

SpicyRice.ttf looks very similar to Duality.ttf, but it is a little thicker. I think many people won't notice the difference. :-)

![yii-captcha-font](https://f.cloud.github.com/assets/100198/293495/a80d5c28-9371-11e2-8184-f54036704d17.png)