Core: attribute U:D:sshPublicKey can be null

Null in value is allowed in the module for U:D:sshPublicKey.

We still don't have something like "optional" attributes for service. So
for this attribute we still need to allow null value in module therefore
the services can mark it as "required" and GEN script must be ready to
get null in this attr.

For services that really reuires not null ssh key, we temporary use
U:D:sshPublicAdminKey attribute.
REGISTRAR: use parsed name when searching for similar users

- When searching for similar users (before new application approval)
  try to parse display/commonName in order to remove wrong input.
  Name titles are dropped from search to provide wider search results.
  If parsing name fails, log, ignore and try to search by whole input.
Merge pull request #137 from zlamalp/reg

REGISTRAR: use parsed name when searching for similar users