* add Remove button

* add Remove button
* post_message(): use IKEY and Flathash, we just use numbers anyway.
* post_message(): add handler for removal of attachments; it seems as if 'filename' comes out URL-encoded, so we need to decode it.
  We need to iterate and strcmp() so we find the right one :(
* post_message(): when adding a new item just using count+1 isn't sufficient anymore; we need to use the key value + 1 of the last item in the list instead