WIP: Refine update progress reports

[joaquimrocha]

I have been working on this PR to make the group's stats a bit more accurate to what the user perceives: the issue is that we are gathering any instances with a certain state (downloaded/downloading/update-granted/error), regardless of whether they are updated or have updated to the version that the group declares. This may hint, for example, that there are 3 instances downloading (the group's version), when they may be actually downloading a previous version, if the group's channel has just updated to a newer package.

Also, instances that have pinged the group and are in the group's version, will have no status change, and this showed up as "undefined" but they're actually instances that are up to date. Another thing that's added is that there was no way to show instances that have timed out, and this patch includes those.

Important: This PR is still missing some important things beyond the charts, like having a way to filter by "time out", etc. otherwise the instances list view will not be accurate.

So this is WIP ATM.

• groups: Replace GetGroupInstancesStats's query by goqu
• backend: Change how the groups' stats are calculated
• frontend: Update circular charts to the match update progress
• frontend: Add a notice to the group's charts area if there's no version