[DevTask] Move base path to desktop app config

[webfiltered]

Current

base_path in extra_models_config.yaml is used as both the desktop install location, and for its original intent - absolute base path of relative model / custom node paths defined in the yaml file.

• Desktop app uses another config file for the rest of its config
• Code is unnecessarily complex
• Users edit the yaml file by hand to add/remove model paths, and a single yaml syntax error will result in the app being unable to launch

Solution

• Rename basePath in desktop config to installPath
• Use installPath in desktop config as the desktop install location
• Use base_path in yaml exclusively for its original purpose

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