Fix 'show-json' command

Wait for retrieval of all item contents before exiting
Add 'show-overview' command to display the overview data for a given entry

  1pass show-overview [pattern]

Displays only the overview data for each item matching `pattern`.

Also sort items case-insensitively in the 'list' command and avoid
showing tombstone entries in the result.
Display human-readable type names for items in 'list' output

Import the item type -> item type name map from the Go 1Password client
implementation.