Classes space update

[Qatavin]

Addresses #620 and #609.

To deal with the issue of Space Age tending to need quite a few different bodies, the maximum height of the Avatar Switcher character list is increased from 250 to 400. Additionally, I reversed the order that characters are listed in. Previously, new bodies and bodies you just switched out of would go on the bottom of the list. Now they go on the top, which should generally be where you'd want them for quick access.

Also, to help with people getting stuck on space platforms and unable to send their characters down to a planet, I have added a message that will show up on the Avatar Switcher box with instructions for how to solve the issue - you need to hit the enter vehicle button to enter the Hub. Then you can rocket down to whatever planet you're in orbit of. This message only shows up when it's needed - when you're controlling a character that is on a space platform but not in a Hub. Hopefully I covered all the bases. Gui stuff still doesn't really make sense to me.

Finally, since I saw it requested somewhere, I adjusted the wording on the Fighter class's description to make it clear that it only gets its special equipment at game start.

Edit:
Addresses #619.

Adds a backup for player-given character names. Now, each player will have their most recent (that is, current) character's name indexes by player name. This is to deal with the issue of character names disappearing due to the Jetpack mod - a consequence of the fact that the character is replaced each time a Jetpack is turned on or off. Now, whenever the gui is updated, it checks whether the controlled character has started or stopped flying. But what if the Jetpack-using character is not the one being controlled? Well, since there's a long-standing issue where the game will crash if a character using a Jetpack lands (runs out of fuel) while not being controlled by a player, I decided to block character switching when you're using a Jetpack. Thus, the only character that can be flying is the one you're controlling.

I also removed the old_character.active = false and new_character.active = true bits from the Jetpack section of the switch_character function. For whatever reason, the game's been changed so you can't write to "active" anymore. I'm pretty sure the entire section from line 1601 to line 1623 can be removed now, since switching is now blocked when you're using a Jetpack anyway.