Json vehicle parts

- Pulled vehicle parts into a JSON file
- Removed the totally unused "par2" field
- Made vehicle part flags an array of strings instead of enums
  - Added a has_flag function to the vehicle part struct to support this
- Made many fields in the JSON optional
- Also allowed the mysterious "par1" field to be accessed by its better, more descriptive names - power, size, wheel_width, or bonus.
- Vehicle part names are now a std::string instead of a char *
- Moved color_from_string out of the item factory and into color.cpp so I wouldn't have to copy and paste it
- Put in a bunch of missing braces while I was at it

I'm hoping that after this gets merged, vehicles can be JSONified next, but we'll have to see about that.