Allow user to specify path to a config file

[wlpotter]

As part of the CLI interactions, allow the user to specify a path to the config file to use. This will let us have a separate one for CBSS, for example

[wlpotter]

To start I've updated to add a $zotero2tei:path-to-zotero-config variable that is external, with a default value of "zotero-config.xml". This means that an external driver can load the module with a separate path (e.g., using the 3.1 function load-xquery-module and passing a map of variable bindings, but it won't interrupt current mechanisms that don't bind the external variable (since it defaults to the current value)