Added a grid style to the bookmarks widget

[Panonim]

This pull request adds a new "grid" display style to the bookmarks widget, allowing bookmarks to be shown as a grid of icon tiles with titles and descriptions, in addition to the existing list view. The update includes documentation, configuration, template, and CSS changes to support this feature.

Bookmarks Widget Grid Style:

• Added a new style option to the bookmarks widget configuration, with support for a "grid" value. When set, bookmarks are rendered as a grid of icon tiles. [1] [2] [3] [4]
• Introduced a new template (bookmarks-grid.html) and corresponding CSS styles for the grid layout, including icon containers, hover effects, and responsive columns. [1] [2]
• Updated documentation to describe the new style option and how to use the grid layout for bookmarks.

Other Documentation and Reference Updates:

• Added a changelog entry documenting the addition of the grid style to the bookmarks widget.
• Fixed a broken link in the "Custom-api widgets" reference in the main README.md.
• Minor cleanup in documentation by removing redundant installation instruction references. [1] [2]