Co-authored-by: Philip Arndt <git@p.arndt.io>

Avoid overriding user's indices

If the models have already been indexed, skip overriding user's
decisions (ie, indexed fields)

Index blog posts' custom teaser

Allow refinerycms-core version from >= 3.0.0 to < 5.0

Use ascii fields for UTF-8 search terms in Page

Allow refinerycms-core version from >= 3.0.0 to < 4.0

Fix user model with new authentication

Fix tests

1. Add placeholder
2. Make placeholder and title html_safe so that html entities can be
used.
3. New i18n string search_input_help used as tootip. Uses wording from
old search_input_notice

Replace wymeditor with visual_editor

Updated Travis CI instructions and fixed specs