Add meeting preview and option to Accept, Decline, Tentavely accept a meeting invitation, for invitations received as a .ICS email attachment

[meetc0]

Checklist

• [X] I made sure that there are no existing issues - open or closed - to which I could contribute my information.
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• [X] I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• [X] This issue contains only one feature request.
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Feature description

Upon opening an email attachment containing a meeting/calendar event invitation, show the contents of the event and provide options to set status to Accept/Decline/Tentative prior to adding into the selected calendar. Send a response to the meeting organizer of the chosen status. Related to #145 #200.

Why do you want this feature?

Right now, there is no way to view a meeting invitation without first adding it into a calendar and searching for it. Support for the status field was recently added with #200.

Additional information

No response