Files, Media and its Replies and things

• Fix size and duration not showing in MimeComponents in replies
• Display Itinerary in replies as MimeComponent (in consistency with media components)
• Fix code preview vanishing after "opening" a file (they get downloaded to /tmp/ without extension, which caused them to lose preview)
• Make all text/plain mimetype files preview
• Don't show code previews in Replies (in consistency with media components)
• Correctly display filename in MimeComponent of file (previously it included the caption)
• Don't append the filename to the caption
• Display filenames and captions in Audio the same as in Video and Files
• Stop assigning undefined to bool in TimelineView and MessageDelegate
• Fix seeking not working in Audio Playback
• show Thumbnail with label when video is stopped

Captions in spec: https://spec.matrix.org/latest/client-server-api/#mfile