Implement "Creative" horse gender with custom behaviour

[Nevakanezah]

Implement a custom horse gender titled "Creative" that can only be applied via commands. Horses bearing this gender gain the following behaviour:

• Able to breed with any able partner, just like vanilla
• Upon breeding, the "age" and "bred" flags immediately reset, allowing immediate re-breeding

This gender should be available in any command that allows gender to be specified or updated, and the /he fabio command should be added to spawn a pre-built horse with this gender applied.

[Nevakanezah]

Incidental - The "Bred" flag on horses might be what triggers partner-seeking behaviour in love mode.