This is transient file that lists functionalities to be implemented before
first major release.

- autocomplete: don't show items that are already used in tag list (unsure)
- posts/upload: ability to paste many urls (unsure)
- posts/listing: add buttons for toggling safety
- posts: fix empty edit snapshots when changing only thumbnail content
- users: add user-configurable "about me" (should support Markdown)
- tags: refresh tags.json when editing post
- tags: add tag merging
- tags: add tag descriptions
- tags: add tag edit snapshots (backed-only)
- misc: endless pager should include information about page number
- misc: add spinner to forms such as registration, login, settings...

- post notes
    - "add note" in sidebar creates new note in the middle of image
    - hovering notes shows note text
    - dragging and resizing notes is always possible
    - clicking note reveals modal popup with textarea to input text
    - under textarea there are buttons for saving and/or deleting the note.
    - post notes should have separate table and shouldn't be stored as json
      column.
    - post notes should be visible in post edit history.
      (move post snapshot factory methods to PostService)

refactors:
    - add enum validation in IValidatables (needs refactors of enums and
      possible disposal of EnumHelper in favor of something more subtle)
    - reduce dependencies