Merge branch 'attachment-handling' of https://github.com/thororm/PrivateBin into thororm-attachment-handling

apart from resolving conflicts:
- added missing docs
- inlined functions that were used in only one location
- updated unit test to support all previews
- fixed a regression that displayed the preview even when there was no preview and too early

i18n/es.json

@@ -132,6 +132,8 @@
     "Cloned: '%s'": "Clonado: '%s'.",
     "The cloned file '%s' was attached to this paste.": "El archivo clonado '%s' ha sido adjuntado a este texto.",
     "Attach a file": "Adjuntar archivo",
+    "alternatively drag & drop a file or paste an image from the clipboard": "alternatively drag & drop a file or paste an image from the clipboard",
+    "File too large, to display a preview. Please download the attachment.": "File too large, to display a preview. Please download the attachment.",
     "Remove attachment": "Remover adjunto",
     "Your browser does not support uploading encrypted files. Please use a newer browser.":
         "Tu navegador no admite la carga de archivos cifrados. Utilice un navegador más reciente.",