[Bf-committers] Import based on extension

[Jan Albartus]

Maybe in a future version Blender could handle importing of files by 
clicking import and blender showing only supported files the user can 
click to import into Blender, instead of the current way of first 
deciding which file to import.

Normally the current works well, but sometimes it's just easier to show 
supported files first and base the selection on which importer to use on 
that. (especially when finding out which format to import works best)

Advantage:
+ More task orientated workflow

Disadvantage:
- Does not show an overview of supported formats