bash: support more 'git notes' subcommands and their options

bash: support more 'git notes' subcommands and their options

The current completion function for 'git notes' only supported the
'edit' and 'show' subcommands and none of their options.  This patch
adds support for all missing subcommands, options, and their arguments
(files or refs), if any.

The code responsible for completing subcommand looks different
compared to the completion functions of other git commands with
subcommands.  This is because of the '--ref <notes-ref>' option which
comes before the subcommand (i.e. git notes --ref <notes-ref> add).

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>