Modify requirement install and add manually load previews

[NekodRider]

• Add civitai_link_logging checks in lib.py and install.py, since sometimes the info spams the console.
• Modify the install process using launch.is_installed and launch.run_pip instead of directly running pip commands.
• Add a manual load section in the settings tab. I think it's common for people to turn off the download on startup and load previews manually after they download some LoRAs. (I used gradio.Dropdown here since I didn't find other ways, please let me know if anyone knows better ways)

[shamblessed]

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