(lsdb-modeline-update): Exclude the case 'net is nil.

(lsdb-modeline-update): Exclude the case 'net is nil.
(lsdb-current-record): Simplified.
(lsdb-current-entry): Simplified.  Don't ask user to select an entry name.
(lsdb-read-entry): New function.
(lsdb-mode-add-entry): Follow the changes of lsdb-current-record and
lsdb-current-entry.
(lsdb-mode-delete-entry): Likewise.
(lsdb-mode-edit-entry): Likewise.
(lsdb-lookup-records): Don't take into account the case that
entry-name is a string.
(lsdb-mode-lookup): Canonicalize entry-name before calling
lsdb-lookup-records.