Enhancement: Follow XDG directory specification on Linux by default

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The XDG Base Directory Specification is based on the following concepts:

• There is a single base directory relative to which user-specific data files should be written. This directory is defined by the environment variable $XDG_DATA_HOME.

• There is a single base directory relative to which user-specific configuration files should be written. This directory is defined by the environment variable $XDG_CONFIG_HOME.

• There is a single base directory relative to which user-specific state data should be written. This directory is defined by the environment variable $XDG_STATE_HOME.

• There is a single base directory relative to which user-specific executable files may be written.

• There is a set of preference ordered base directories relative to which data files should be searched. This set of directories is defined by the environment variable $XDG_DATA_DIRS.

• There is a set of preference ordered base directories relative to which configuration files should be searched. This set of directories is defined by the environment variable $XDG_CONFIG_DIRS.

• There is a single base directory relative to which user-specific non-essential (cached) data should be written. This directory is defined by the environment variable $XDG_CACHE_HOME.

• There is a single base directory relative to which user-specific runtime files and other file objects should be placed. This directory is defined by the environment variable $XDG_RUNTIME_DIR.

At present, Cortex by default creates its own folder in the root of the home directory. This can be configurable however it would be better if we follow the specification by default.

More information: https://specifications.freedesktop.org/basedir-spec/latest/