Allow defining default names for portraits

The name is the last value of an `option` key in `engine/hero_options.txt`.
Example: `option=male,head_short,male01,The Hero`

This means that the `default_name` variable in `engine/misc.txt` is now
obsolete.
Merge pull request #352 from dorkster/joystick

Allow defining default names for portraits
Merge branch 'master' of https://github.com/clintbellanger/flare-engine
Adapted to new default name implementation.