Add prompt for reason creating new description segment variation

[CSchmitz81]

When adding a new description segment variation, add a prompt asking why the segment variation was created. There should be a shared list of reasons from the segment behavior, and reasons from each type. Reasons should each have a unique ID, which is how they would be saved in data, and the string would be looked up using the ID when needed. The IDs for shared reasons should have enough room to grow (probably no less than 99 or 0xFF IDs), and IDs can be reused between different segment types, as long as the value doesn't overlap with the shared behavior reason IDs. A reason must be included to be a valid segment, and we may want to also include the ID of the variation being changed so it can be compared.