Make DM list 150x more stable

[cyyynthia]

This update will also change the behaviour of the list itself, but in a good way:tm:

• The list is the Discord's list, with extra components. I found a (fucky) injection path that allows me to inject just before the scroller.
• Component of the list is Discord's PrivateChannel. less classes to deal with, and it's populated thanks to Flux.
• Favourite Friends items are just "shortcuts". They'll open the actual DM channel, and favourite channels are still available in classic list.
• So to make it not pure repetition the Favourite Friends section is collapsable.
• Fixed most issues, including when there is no DM channel opened, BetterFriends will open it for you and redirect to the channel