[FIX] base_import: improve image feedback & remove image URL restriction

* If the item is not an acceptable URL, check if it's base64 and
  return an error if it's not, otherwise it just ends up blowing later
  when the content of the field is assumed to be base64 and explodes
* The URL having to contain png or jpg or tiff or gif or bmp doesn't
  make much sense (especially in this modern world where
  placekitten.com doesn't add extensions, not to mention this doesn't
  actually check for extensions). After discussing with odo it doesn't
  seem to have any security impact, the only thing this filter does is
  annoy people for no reason.

0 files changed, 0 insertions, 0 deletions