v2.9.1 for KSP 1.12.x

What's Changed

• Lower leader removal costs by @NathanKell
• Fix a number of issues with crew training. Add a toggle to hide researched but not-purchased parts; don't allow mission training for any but purchased parts; fixed mission training not appearing on part purchase until a scene reload; and remove training options when a research is canceled on a tech by @NathanKell
• Fix trainings ignoring different part types if the only difference was the additional time; instead the additional time was being ignored. Now parts have their proper training lengths and aren't improperly combined (notably, the stock landercans) by @NathanKell
• Lower the Tracking Station requirement for Early Inner Planet Probes by @NathanKell
• Lunar Mapper (optional) contract now requires data on 8 biomes, rather than 1 by @ppboyle
• Fix Airlaunch Launch Azimuth not persisting by @siimav
• Fix being able to start a training course with no nauts selected by @NathanKell
• Fix display of leader retirement and can-remove dates by @NathanKell

Full Changelog: v2.9.0.1...v2.9.1.0