Expand the share models and create a new auth model

Newly required:

• shareDisplayName: meaningful optional label for the share that is displayed to the user

Consider:

• The shares have an authType property. Should it remain this way?

The new idea is that each share (whether managed by MDM or set up locally) can have its own authentication information (username/password, Kerberos auth info, etc.). There will therefore be a separate model with the (possibly) different authentication information. The actual username/password information should be stored in the keychain, while the metadata (what is linked to what) will be stored elsewhere (e.g., UserDefaults).

The primary task to be addressed is the link between shares and the new authentication model.