Update 0.19.0 - New difficulty mode and QoL improvements

Hey everyone!

Here goes the last, slightly bigger update before we reach 1.0 :)
It contains the missing "Challenge" difficulty mode, rename/delete options for save slots and other requested quality of life improvements.

Changelog v0.19.0

"Challenge" difficulty mode has been added with these modifiers:

• You will lose 20% exp and 8% of your coins upon defeat.
• Enemy density is increased by roughly 50%.
  (This primarily affects the overworld levels)
• Recovery at bonfires is disabled.
• Fast travel cost is increased.
• Your starting health is slightly decreased.
  (This primarily affects the overworld levels)
• Enemy base level is increased by 1.
• Auto-recovery is disabled.
  (Recovery from herbs, potions, etc. still works as normal)

Other improvements and fixes

• It's now possible to rename and delete save slots within the game.
• The current difficulty is now shown in-game in the statistics view.
• It's now better indicated in the character view if you reached the max player level of 25.
• The attribute tooltips now include detailed numbers of the affecting bonusses, like base value, equipment bonus, and other bonusses.
• A problem with custom keybindings has been fixed, that caused the previous key to still trigger the action that has been assigned to a different key.
• Multi-threaded rendering has been enabled, which should increase performance on mid and low end systems.
• Interactive objects in the world can now be highlighted by keypress (default ALT).
  Please note that it's possible that you need to rebind this key in the options, if you already changed other keybindings.
• The game now automatically keeps 1 backup of your last savegame.
  If you run into any issues with your savegame, you can now manually restore it in the save folder.
  However, this will most likely never be necessary :)