Change argument for Message#setStreams back to List<Stream>

This was b0rked in commit ab4e8caa8c8256b5236fc63a190c7aaa63588d70.
Custom exceptions should never inherit from Throwable directly
Set invalid (but non-empty) password for accounts synced from LDAP

Accounts which have been synced from an LDAP directory had an password by default.
Unfortunately our validation didn't take this into account and the automatic creation
of the user account in Graylog2 subsequently failed.

User accounts synced from an LDAP directory will now get an invalid but non-empty
password. This prevents the failing of our validation but still prevents users from
logging into Graylog2 when the LDAP server isn't available.

Fixes #661
Don't check open file limit on Elasticsearch nodes running on Windows, fixes #715
Use the right collection for dashboard positions
Add null-check for Elasticsearch node "os.name" (just in case)
Merge branch 'master' into config-bundles