add background image blur feature

[afterl1ght]

add image gaussian blur for anyone who wants it

• [x] add background image blurring feature (modify Image blur radius in tools > options
• [x] works with or without Expand To IDE
• [x] fix inaccurate colors due to incorrect pixel format (affects both Blur and SoftEdge)

[!WARNING]

• WebApi slideshow images somehow load much slower between images while Image blur radius > 0. it still works with no performance problems so far, but i don't recommend using image blur during WebAPI slideshows.
• does not support GIFs and videos.
• localization: BlurRadiusDes description for JP and CN are missing.

i initially modified this for personal use because i want to fake mica effect. and also it looks cool!

image previews

[buchizo]

@afterl1ght Thank you for your PR ;)

[buchizo]

ver 3.1.23 is include this feature: https://github.com/buchizo/ClaudiaIDE/releases/tag/Release3.1.23