feat: add options to control window bar alpha

[Samillion]

Fixes: #307

Changes:

• Remove deprecated title_bar_box option
• Fix window_fade_alpha behavior to work properly. (0 to disable)
• Add window_fade_blur_strength to control window bar blur strength separately from osc

# alpha of the window title bar (0 to disable)
window_fade_alpha=75
# blur strength for the window title bar. caution: high values can take a lot of CPU time to render
window_fade_blur_strength=100