Pattern scale option on toolbar

This adds a slider for changing the Texture Scale to the main toolbar (in "Brushes and Stuff").

Compiles and runs, and feature works as intended.

This is a feature that I've wanted for quite a while, and I think I've seen it requested by others on krita-artists.org. It makes texture brushes (e.g. y)_Texture_Reptile) much more usable, since going into the brush settings every time you want to change the size is a pain. It works just like the Size, Flow, and Opacity options in the Brushes and Stuff toolbar. I added Texture Scale as a fourth option to brushSlider1 - 3, and also added brushSlider4, so users can have all four options if they want.