Tooltip contains 'Unable to determine date'. Fixes #6395

$userId is now a mandatory parameter for searchByTags.

Also fixed some places in the code where the argument was missing (Node
API and View)

In some cases a "NotFound" might be expected, so just return false as
before. But for other exceptions, the exception is now logged.

Local change 283c10f0

Local changes from d069ee8a
and 258ad38f

Local changes copied from ed835973
and 25370fcb

Only fixed in Local by eeee9eac

Missed in 788c8540

In some cases the 'size' field is not available resulting in some PHP errors such as:

```json
{"reqId":"03548fd9e3d3aca15a5796b3b35d7b9d","remoteAddr":"::1","app":"PHP","message":"Undefined index: size at \/Users\/lreschke\/Programming\/core\/lib\/private\/files\/fileinfo.php#125","level":3,"time":"2014-11-17T21:38:57+00:00"}
```

This can be experienced when creating a new empty file and deleting it right away, then when going to the trash bin this error is thrown.

Either we throw an exception or we ignore it. But we should certainly not print this to the end-user...

Added missing cleanPath() call that converts "/" to "" when calling
SabreDAV. This is needed because SabreDAV will discard its base URL when
passing "/".

It's only reasonable to have proper type hinting here which might even help us to catch bugs.