Show calendar-icon instead of paper clip for iCalendar attachments

Checklist

• I have used the search function to see if someone else has already submitted the same feature request.
• I will describe the problem with as much detail as possible.
• This issue only contains a request for one single feature, not multiple (related) features.

App version

6.202

Problem you are trying to solve

For an email with structure:

Content-Type: multipart/alternative
    Content-Type: text/plain; charset=UTF-8; format=flowed
    Content-Type: text/html; charset=UTF-8
    Content-Type: text/calendar; charset=UTF-8; method=PUBLISH; component=VEVENT

Gmail shows a calendar symbol in the list of emails in Inbox, near the end of the line. Evolution also uses a specific icon for invitation in its Attachments column.

K-9 shows paperclip symbol in the list of emails (Inbox-view, not reading a single email).

Suggested solution

In this case K9 shall show a Calendar icon instead of a paperclip 📎 icon.

As extra-feature, when the component=VTODO K9 shall show instead a task icon.

Screenshots / Drawings / Technical details

No response

Start by locating the Inbox email-list rendering for attachment icons and the handling of text/calendar parts, using the reported multipart structure as the case to trace. Done means iCalendar VEVENT attachments use a calendar icon instead of the paperclip; the optional VTODO case uses a task icon.