Icons, fixes, link preview panel, experiments

Additions

• Styled the new link preview panel.
• Added icons for image search and link preview entries in the context menu.
• Added a staggered slide-up animation for downloads when using uc.winui.experiments.

Adjustments

• Fixed link colors.
• Fixed the position of floating tabs windowed titlebar button glyphs.
• Standardized card style for built-in extensions page.