Ensure table values are always strings

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Remove assumption that a report generates a single table

Introduce a ReportOutput class for outputting report results
in text/json/xml. Add a ReportTable subclass for tabular
data and adapt all existing reports to use this new approach.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Add support for compound report output with titles

Add support for generating compound output sections with
titles and use this with the patchreviewstats command

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Split format_date function for a separate format_delta function

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Implement a 'openreviewstats' command

Provide a 'openreviewstats' command to provide information
about changes that are waiting for reviewer attention.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>