Install letter-opener.

This automatically opens up received emails in the
browser.
Update version to 1.1.0.rc1.
Merge in changes regarding versioning.
Move search views out to engine.
Add missing migration to ose.
Merge remote-tracking branch 'origin/1.1.0.rc1-advanced-search' into 1.1.0.rc1

* origin/1.1.0.rc1-advanced-search:
  Move search views out to engine.
  Update version to 1.1.0.rc1.
  Install letter-opener.
Merge remote-tracking branch 'origin/1.1.0.rc1-mailchimp-migration' into 1.1.0.rc1

* origin/1.1.0.rc1-mailchimp-migration:
  Add missing migration to ose.