Fix image position of newest media in home
Rename default media.ctp element view to media_full.ctp
Make explorer view configurable system wide and per user

Explorer view can be configured for page size, sort order and
media view. The system operator can configure system default and
users can overwrite them by their own setting.
Write user data into session

Before only the user id was written to the session and the user
data was queried on each request.
Code style cleanup