Improve bold DEC Special Characters rendering

On Linux (not sure for other OS), Swing rendering of bold graphical characters is terrible.

This is a workaround, using heavy flavour of these characters, instead of bold style.
I've made it an option; there is no impact if this option is set to `false`.

Below is a comparison with the option activated (left), and deactivated (right) :

![decspecialcharsworkaround](https://f.cloud.github.com/assets/3908084/1353607/f4cee930-3747-11e3-8a79-6f442d33b7df.png)