#117 MIME attribute support

[Anonymous]

It seems there is no MIME attribute. It is possible to see
attached pictures or others because SimpleMail uses
DefIcon to find the filetype but :
- what about users that don't have deficon (MorphOS
users). MIME would be more standard
- about videos : the datatypes are used to play videos
using datatypes, so the results are rather poor :( I
would be nicer to choose an external viewer depending
on the file type.