Further reworks to melee stances (fencing, balanced, block)

Melee stances have improved since the release day versions, but I think they still need work to make each choice appealing, specifically the block stance.

I suggest adding more emphasis to a "block window" that complements the parry window. Essentially, the fencing stance will be all about parrying attacks, whereas blocking will be about perpetually blocking in place until ready to strike. Fencing allows the player to parry attacks with a wider window, blocking allows the player to retaliate after blocking by releasing an area of effect (AOE) that staggers enemies. The blocking AOE can become stronger as the player blocks more attacks, but it can essentially be released even after one attack. The stronger the block charge is, the larger and stronger the AOE is with its potential to stagger. This gives both fencing and blocking access to stagger and gunstrikes while making the stances feel different. 

The balanced stance is a merger of the two other stances where there is a short window for parry and a short window of blocking (somewhat similar to how it works now), but the block cannot be held.

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Overall, I think this would make blocking a more appealing stance and would provide more benefit to chaos missions where players deal with a lot of ranged attacks.