Fixes strange Yrden scaling introduced in patch 1.10.
Backstory:
If you reach 100% Yrden slow you freeze enemies, so in 1.10 CDP introduced a fix :
- Fixes issue whereby Yrden with elevated Sign intensity would cause foes to freeze

So how did they fix it ? You would think they caped it at 80% or 75% or whatever.
Nope, they caped it at 42% (why this number?) and nerfed scaling so much its pointless to even think about it.

Some math and code here :
http://forums.cdprojektred.com/threads/59075-Yrden-Scaling-Nerf-%28Bug-%29?p=1935126&viewfull=1#post1935126

As of patch 1.10 Yrden scaling is VERY poor :
You start game with 25% Slow @ 0 spellpower
You cap Yrden with just 42% @ 295 spellpower

Total Yrden scale range is 17% and that cost you 295 spellpower.
I dont know what CDP was thinink but that is just silly.
Without Yrden, Sign build is just 1 button normal Igni spam.

So I fixed scaling to being similar to 1.8 patch but cap it at 80% to keep "bug" out.
With this scaling you get :
Start game 24% @ 0 spellpower
Cap is 80% with ~300 spellpower (little harder to reach 80% than 1.8)

Alternate Yrden no change.

Modified files :
1. \content\scripts\game\gameplay\items\spells\yrdenEntity.ws (to acualy change power when casting)
2. \content\scripts\game\gui\popups\CharacterStatsPopup.ws (to correcly show new % in stats)