Adds text reference migration
Extracts text reference update methods
Considers host name in settings
Adds support for host postfixes
Removes changeset migration

Changesets represent VCS commit messages. Thus, there is no point
migrating changesets because we do not migrate VCS commit messages as
well.
Adds changelog entry
Removes migration of text references in journals
Makes test reference migration the last one
Uses original timelines regex
Resets journal primary key after migration
Extends column update interface
Ignores pre/code blocks
Adds WP journal entry for text migration