* create dropzone for editing in jot-modal
* customize css for dropzone to make it more beautiful (smaller
margin/paddings...)
* change position of dropzone-element dircetly to textarea, so button
for upload is small and under textarea (it's more clear)
* remove previews after upload. this shows the upload-progress, but
preview is not needed after upload. you can't do anything with the
preview, and dialog gets too big. You see successful upload, when
bb-code link to image is inserted on cursor-position in textarea
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