[FEAT] Manage isUserSelectable = 1 ; Is the plane selectable by the user

[wdmaxq]

Description

Installing a ton of liveries for AI use tremendously clutters the select livery for user aircraft screen

Solution

Allow the Livery Manager to change the isUserSelectable variable in the aircraft.cfg files, based on a simple checkbox in the Livery Manager for each installed managed livery.

Why is this the best solution?

This would allow a ton of AI liveries to be available, while at the same time declutter the user aircraft livery selection.