Codechange: [Script] Use helper function over direct casting CompanyID

In the script's API `COMPANY_INVALID` has a value of -1, whereas the internal
game's `INVALID_COMPANY` has a value of 255. Since the script's API also has
a `COMPANY_SPECTATOR` with a value of 255, these enumerations cannot be easily
reconciled by casting. As such, replace all casts in the script API with
either ScriptCompany::FromScriptCompanyID or ScriptCompany::ToScriptCompanyID.

Also make clear whether CompanyID is ::CompanyID or ScriptCompany::CompanyID
by using either one of those over CompanyID in the script's API.

src/script/api/script_controller.hpp

@@ -52,7 +52,7 @@ public:
 	 * Initializer of the ScriptController.
 	 * @param company The company this Script is normally serving.
 	 */
-	ScriptController(CompanyID company);
+	ScriptController(::CompanyID company);
 
 #else
 	/**