Fix db:populate and Event#set_author_as_organizer after c12c507236

Event#set_author_as_organizer only adds the author as organizer if there is
an author set.
db:populate was failing because it wasn't setting an author for the events.

refs #383
Simplify and refactor spams in general, refs #455

* Remade the management view using common classes and partials
* Removed what could be removed from the controller and views
* db:populate now generates a few events and posts marked as spam
Several small improvements in the form to add posts

* Use simple_form
* Move strings to the correct places in the locale
* The inputs are only hidden when the button 'cancel' is clicked or ESC is
pressed -- less confusing, more reliable
* Improved the visual