UserApp: Fix server error caused by OptimisticLockException

OptimisticLockException occurred occasionally when
UserApp.updatePreferredLanguage() is called.
Merge branch 'fix/user-lock-exception' of dlab/hive

from pull-request 1376

* refs/heads/fix/user-lock-exception:
  UserApp: Fix server error caused by OptimisticLockException

Reviewed-by: 백기선 <keesun.baik@navercorp.com>
PullRequest: Fix a bug that cannot update pullrequest

Reason: The ref to the merge commit could not be updated because
force-update was false.
Merge branch 'fix/cannot-update-pullrequest' of dlab/hive

from pull-request 1384

* refs/heads/fix/cannot-update-pullrequest:
  PullRequest: Fix a bug that cannot update pullrequest

Reviewed-by: 김덕홍 <insanehong@navercorp.com>
Add the release notes for v0.7.1
Merge branch 'docs/relnotes-0.7.1' of dlab/hive

from pull-request 1385

* refs/heads/docs/relnotes-0.7.1:
  Add the release notes for v0.7.1

Reviewed-by: 김덕홍 <insanehong@navercorp.com>
Yobi 0.7.1

Fix a critical bug that cannot update pullrequests

Reviewed-by: insanehong <insane.hong@navercorp.com>