Season and holiday configuration options (#138)

* Added configuration options to change the season and holiday (per-server and globally) in config.json
* Added documentation on newly added configuration options
* Updated parseHoliday to recognize all current holidays
* Moved parseSeason and parseHoliday functions from server/commands.ts to common/utils.ts

config-template.json

@@ -19,6 +19,8 @@
 		}
 	},
 	"assetsPath": "assets-source",
+	"season": "spring",
+	"holiday": "none",
 	"servers": [
 		{
 			"id": "test",
@@ -26,6 +28,8 @@
 			"path": "/s00/ws",
 			"local": "localhost:8090",
 			"name": "Test server",
+			"season": "spring",
+			"holiday": "none",
 			"desc": "Testing server",
 			"flags": {
 				"test": true