Editor improvements (#486)

- Make it possible to insert new paragraphs in the article body
- Make it impossible to copy formatted HTML (to make media insertion from markdown code work correctly)

TODO:

- [x] make it possible to escape draft mode
- [x] display errors from the server
- [x] button to go back to the "normal" editor
- [x] Avoid publishing placeholders

po/plume-front/en.po

@@ -12,6 +12,10 @@ msgstr ""
 "Content-Transfer-Encoding: 8bit\n"
 "Plural-Forms: nplurals=2; plural=(n != 1);\n"
 
+# plume-front/src/editor.rs:110
+msgid "Open the rich text editor"
+msgstr ""
+
 # plume-front/src/editor.rs:57
 msgid "Title"
 msgstr "Title"
@@ -40,6 +44,10 @@ msgstr ""
 msgid "Cover"
 msgstr ""
 
+# plume-front/src/editor.rs:167
+msgid "This is a draft"
+msgstr ""
+
 # plume-front/src/editor.rs:111
 msgid "Publish"
 msgstr ""