/gcal viewcal and daily summary show up declined events

[fmartingr]

The current implementation of the /trigger viewcal and the daily summary show up declined events for Google Calendar. For consistency, we should make it so declined events do not show up in those command results.

Acceptance criteria

• Using /gcal viewcal will show up only events that are not declined. (Accepted, Tentative, not-answered)
• The daily summary should not display events that are declined.

Related tasks

• Improve layout of viewcal command mattermost-plugin-mscalendar#325
• Review viewcal command dates or help text mattermost-plugin-mscalendar#315

[hanzei]

1/5 that declient events should also show up but should be marked as such. That way users can double check if they really wanted to decline the meetings.