Avoid fetching particles.json each time the theme is switched

[nishant-nayak]

The logic for updating the Particles config on the public facing pages needs to be fixed in dark_mode_toggle.html. The current logic fetches the particles.json everytime the theme is switched. This leads to unnecessary network calls and visible lag in the particles after many changes.

The logic has to be updated to either updated the config without a config file (directly modifying the JS parameters) or fetching both files once and storing them locally for each switch.