'snap info' should show date of release into channel

[Mark Shuttleworth]

Snap info is a great way to get a sense of the level of activity behind a snap, especially the map of channels and released revisions. It would be improved however with the addition of the date on which a channel last changed with a new release to that channel. For example:

$ snap info etcd
name: etcd
[...snip...]
channels:
  stable: 3.2.8 2018-03-22 (76) 11MB -
  edge: 3.3.0-rc.0-391-g3239641 2018-03-24 (111) 12MB -
  2.3/stable: 2.3.8 2017-08-15 (55) 5MB -
  3.0/stable: 3.0.17 2017-04-02 (85) 10MB -
  3.1/stable: 3.1.10 2017-09-13 (81) 10MB -
  3.2/stable: 3.2.9 2018-02-23 (108) 11MB -
  ingest/stable: ingest-0.5 2016-09-18 (12) 4kB classic

Also note the right-alignment of the revision and size columns in this example.

[John Lenton (chipaca)]

https://github.com/snapcore/snapd/pull/6337 FWIW

[Mark Shuttleworth (sabdfl)]

Excited to have this, thank you John! It will make 'snap info' much more
telling about the level of activity in the snap.

Mark