Upload dialog should allow only context specific files

Example in categories app:

1. Click on 'Import' in action bar
2. Click on 'Upload'
3. File chooser allows me to pick any file
4. Upload an image from desktop
5. Click 'Import' button
6. Red error banner pops up behind the dialog

To upload an image doesn't make sense in this context.

This is overall a bad User experience.

Expected behavior:

Either: not allow to pick wrong files from the desktop in the first place

Or at least: Show error message right after selecting the file.

• Show error message on top of the popup, not behind.
• Use simple and user friendly language for the error message