Initial support for adding non-login item types via the CLI

The syntax for adding an item is now:

  add <item type pattern> <title>

If there are multiple matching item types, the user is prompted
to select one.

For non-login item types, the newly created item is currently
empty and any sections and fields will have to be added via
the 'edit' command.
Add an empty default section to new non-login items

This makes it more convenient when adding subsequent fields
using the 'edit' command.