fix: 🐛 activate liquidprompt preset after sourcing

[tkapias]

To be activated after being sourced, Liquid Prompt needs to run the function lp_activate.

This PR adds it at the end of the preset file.

Some styles where added and changed also.

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I may write an issue with some documentation for the wiki later, in short the most easy way to run Liquid Prompt is to source some files with bash or zsh:

1. An optional config file with custom settings.
2. The main Liquid Prompt script.
3. An optional preset script like the Falcon one, ending with lp_activate.
4. An optional theme script for the layout, activated with lp_theme theme.