Going forward for new installations, config and data files will be
stored at the platform default paths, as defined by
[env-paths](https://www.npmjs.com/package/env-paths).
For backwards compatibility, if the `~/.waveterm` or `WAVETERM_HOME`
directory exists and contains valid data, it will be used. If this check
fails, then `WAVETERM_DATA_HOME` and `WAVETERM_CONFIG_HOME` will be
used. If these are not defined, then `XDG_DATA_HOME` and
`XDG_CONFIG_HOME` will be used. Finally, if none of these are defined,
the [env-paths](https://www.npmjs.com/package/env-paths) defaults will
be used.
As with the existing app, dev instances will write to `waveterm-dev`
directories, while all others will write to `waveterm`.
