vte/font/console: support basic character attributes

vte/font/console: support basic character attributes

This adds support for colored and bold characters. This also adds the
infrastrucure for background colors and underlined characters, however,
these are not properly implemented, yet.

The color codes are similar to xterm and optimized on black backgrounds.
So they are not too bright or shiny.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>