Use count SQL to check for user existance
Use the MDB2 function to get the count result
Handle empty datafolder better.

If datafolder is erased, the default value will be shown as a placeholder.

If installation is submitted without a datafolder the default value will be used.
fix navigation hover effect, documentation
additional comments
Hint to default data directory

not to before submitted data directory.

Thanks to bartv2 for the heads up.
Merge pull request #2915 from Kondou-ger/handle_empty_datafolder_better

Handle empty datafolder better.
improved free space calculation if no quota is set, discussed in #2936
adapt free space calculation to the way it is done for the trash bin
Merge pull request #2746 from owncloud/use-count-userexists

Use count SQL to check for user existance
use date and time instead of timestamp
fix admin log display and use a more readable format
Remove not null constraint. Fix #2976
also adjust template properly for log date fix
Merge pull request #2975 from owncloud/log-date

use date and time instead of timestamp in log
Merge pull request #2978 from owncloud/displayname_can_be_null

Remove not null constraint. Fix #2976
apply navigation hover effect directly to img and span, cleaner code
Merge pull request #2925 from owncloud/navigation-icon-fix

fix navigation hover effect, documentation
Warn when we do an upgrade
Merge pull request #2986 from eMerzh/upgrade_warn

Warn when we do an upgrade