Add functions in server GUI

Add AI enum table
Add some missing functions

library/mission/airbase.lua

@@ -0,0 +1,16 @@
+---@meta
+
+---@class Airbase: CoalitionObject
+---@field id_ integer
+Airbase = {}
+---@enum Airbase.Category
+Airbase.Category = {
+    AIRDROME = 0,
+    HELIPAD = 1,
+    SHIP = 2,
+}
+
+---Returns a localized string of the airbases's callsign.<br>
+---In the case of airbases, the callsign of world airbases is defined by the game. Callsigns for units, farps, or ships can be specified by the user with the mission editor or scripting engine.
+---@return string
+function Airbase:getCallsign() end