Drastically simplified the Quest Log system.

I removed the unique quest key from the quest log entries
and made the completion events be part of the quests.lua file.

I also lighten the MenuView::Update() and Draw() calls, making
the check for completion only done when opening the quest list window
for the first time.

I also moved the completion check into the global manager and removed
redundant or used once functions.

Finally, I added a small green check in front of completed quests.