Blur Perfected

This update expands the functionality of Blur+ to be more consistent throughout the game, and more configurable.

Changes:

• new feature that let's you select different animation curves for the background gradient and/or blur animations
• fix blur slider not working past 10 (broken again by the upstream blur+ 5.3.2)
• new feature that let's you toggle blur for Book edit/view/sign screen, Command Block edit screen and Sign edit screen separately, these screens were not previously blurred at all by the upstream blur+ 5.3.2
• optimization for not drawing background gradient or blur animations when it's not noticeable
• fix a bug where disabling gradient background would not disable it in some scenarios