[Suggestion] Changed the season definition when using isSeasonTiedWithSystemTime to be more realistic

[jaoreir]

Why the change

I like when games sync the seasons to real life, so I enabled the config option isSeasonTiedWithSystemTime, but I find it strange that winter starts on the end of December, instead of somewhere near the start.
So I changed the definition of seasons when using that option to be more realistic.

Original definition

Northern Hemisphere

• Spring: 3/20 ~ 6/20
• Summer: 6/21 ~ 9/21
• Fall: 9/22 ~ 12/20
• Winter: 12/21 ~ 3/19

Southern Hemisphere

• Spring: 9/22 ~ 12/20
• Summer: 12/21 ~ 3/19
• Fall: 3/20 ~ 6/20
• Winter: 6/21 ~ 9/21

New definition

In the north, spring is slightly longer, and fall is slightly shorter because of the earth's elliptical orbit.
(The specific dates were adapted from other games.)

Northern Hemisphere

• Spring: 2/25 ~ 5/31
• Summer: 6/1 ~ 8/31
• Fall: 9/1 ~ 11/25
• Winter: 11/26 ~ 2/24

Southern Hemisphere

• Spring: 8/25 ~ 11/30
• Summer: 12/1 ~ 2/28
• Fall: 3/1 ~ 5/25
• Winter: 5/26 ~ 8/24

[lucaargolo]

I like these changes. I'll probably add another config option so you can choose between the new definition and the old one.
As soon as I have time, I'll review and merge this.