patman: Support checking for review tags in patchwork

patman: Support checking for review tags in patchwork

Before sending out a new version of a series for review, it is important
to add any review tags (e.g. Reviewed-by, Acked-by) collected by
patchwork. Otherwise people waste time reviewing the same patch
repeatedly, become frustrated and stop reviewing your patches.

To help with this, add a new 'status' subcommand that checks patchwork
for review tags, showing those which are not present in the local branch.

This allows users to see what new review tags have been received and then
add them.

Sample output:
   $ patman status
     1 Subject 1
       Reviewed-by: Joe Bloggs <joe@napierwallies.co.nz>
     2 Subject 2
       Tested-by: Lord Edmund Blackaddër <weasel@blackadder.org>
       Reviewed-by: Fred Bloggs <f.bloggs@napier.net>
     + Reviewed-by: Mary Bloggs <mary@napierwallies.co.nz>
   1 new response available in patchwork

The '+' indicates a new tag. Colours are used to make it easier to read.

Signed-off-by: Simon Glass <sjg@chromium.org>