use json_encode for json lists

various params have to be tweaked to be more meaningful and / or handle
null cases
submodules update
update partials cache

- _feature partials have been removed, so entries are obsolete
- json list of associated parkings shouldn't be cached
json lists: provide better info

- give meaning to some numeric fields (e.g. activities)
- correctly handle doctrine null values
cleaning
pretty print json output
enable photo upload for recent mobile devices
plupload: explicit HTTP error code