Adding Favourites as another tab

I added another tab to Loot Navigation panel called Favourites,
as well as corresponding boost. Player can enter names or aliases
of up to 20 boosts, and remove them on the one by one basis. List
is stored in savefile, and also gets exported//imported.

Further testing may be needed, as well as considerations for price
or unlocking requirements, and general boost format.

UPD: Related boost still may not behave and appear as intended in many cases, so use ````Molpy.Boosts['favs'].unlocked = 1 ```` to see it in the shop.