Added more textures and a proper preview image

The textures brushes haven't been out that long, but there were a few other patterns I came across while experimenting with them. To save myself time I made my favorites into brushes too.

There has also been a new preview image added so everyone can see the textures inside, along with the Sai v1 install instruction file updated to match the changes. Speaking of, any Sai v1 users that want to update to these will want to delete "Pixel Floral" because there is now "Pixel Floral A" and "Pixel Floral B". There won't be any conflicts, it's more just removing duplicates so up to ya'll if you do it or not.