Add customising of save location

Currently ljArchive defaults to saving to My
Documents\ljarchive.lja, and if the user wishes to save
the file elsewhere they need first to navigate to the
desired drive/folder.

Adding a "save in folder" element to the archive setup
dialog would enable the user to specify their preferred
archive location once, with the program then prompting
with that as the default location for subsequent new
archives. It would also separate out file location and
file name, making it easier to give the file a name
other than the default ljarchive.lja.