models: add SeriesMerged event
models: add SeriesMerged event

This can be used to send email when a patch is applied.

Reviewed-by: Fam Zheng <3fda8cf018b542f405493d78ea980b2545014644@euphon.net>
Signed-off-by: Paolo Bonzini <69d3ebcf5ee4e7f05a50dc23cd96655b730804b4@redhat.com>

pvital/patchew,pvital/patchew,pvital/patchew,pvital/patchew