Minor clean-up after that last patch.
Issue #1958122 by fietserwin, herved: Pathologic should handle not yet created image derivatives as if they are files
Issue #2628348 by jurgenhaas: Language prefix is not split off because of caching
Make local settings actually work as they're documented. Oops.
Issue #2597279 by giancarlosotelo: Add UI tests
Issue #2608102 by giancarlosotelo: Replace !placeholders
Update drupal.org URLs in links.
Fix phrasing of "input format" to "text format"
Fix hiding of local settings form on the filter settings form until the user selects the "Use custom settings" radio button.
Update URL to Pathologic documentation page on Drupal.org.
Issue #2596361 by giancarlosotelo: Replace ! placeholder with : in settings form
Delete pesky invisible character from comment.
Issue #2575361 by giancarlosotelo, miro_dietiker: Settings form submit fatal error
Issue #2562489 by giancarlosotelo: FIx config schema error: pathologic.settings:langcode missing schema
Issue #2415771 by das-peter, ordermind, Garrett Albright: Trouble with Entity Translation and embedded node links
Make sure our new PathologicEntityTranslationTestCase doesn't cause fatal errors when Entity Translation module isn't installed (because the parent EntityTranslationTestCase won't exist).
Issue #2538928 by mbovan: <front> is not implemented correctly
Issue #2471577 by LKS90: Replace all occurrences of String class with the SafeMarkup equivalent
Issue #2477221 by Johnny vd Laar: Featurizing pathologic when pathologic has been used in hook_init
Fix new error when trying to show configuration form.
Fix global settings.
Fix running of tests given new configuration weirdness. Tests still fail, but at least they complete.
Get the filter settings form to work as it does in the D7 version, and also get all the D8 configuration stuff patched up. I hope this all works now.
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