Optimize the search system

[GianlucaCise]

Add a filtering system in the search tab.

• Create a search tab (substituting the lateral panel)
• Add a tag system (eg. Categories, Software, exc...)

[nodiscc]

I have been looking at https://github.com/typesense/typesense which, as far as I remember, can be integrated into our existing toolset (sphinx-doc) and would improve (currently mediocre) plaintext search results.

The search UI will probably stay as it is though (the searchbox in the lateral panel is fine).

The tag system is already implemented.