Fix two bugs, change DB schemas, add test coverage.

Bug fixing:
 * Fixes bug on PictureSet 'order' field. Pictures were not ordered as
   expected. Now the are shown in the order specified in both, the inline
   and the slider.
 * Fixes bug when applying INLINE_MEDIA_TEXTAREA_ATTRS setting.
DB schema changes:
 * Picture Model gets new field 'show_description_inline' that allows
   user disable showing field 'description' in inlines, although still
   visible in prettyPhoto slider.
 * PictureSet Model gets two new fields: 'show_description_inline' and
   'show_counter'. The first has pretty much the same functionality as
   for the Picture model. While 'show_counter' allows the user disable
   showing the counter of pictures in the inline.
Test coverage:
 * For the two bugs fixed and for new model fields.
Todo:
 * Start to write a ChangeLog.