Allow config file location to be passed to commands

[nblumhardt]

Currently the location of SeqCli.json is fixed; ideally commands would accept --config="<path>" to override this location.

[mloskot]

On Linux, it would also be useful if the configuration file location respected XDG_CONFIG_HOME or just follow the common convention with $HOME/.config/SeqCli.json or $HOME/.config/seqcli/config.json, by default.

[nblumhardt]

Implemented via SEQCLI_STORAGE_PATH 😎