feat(17-01): richeditor field type on the seaglass sanitizer

- seaglass (new module): bluemonday v1.0.27 policy ported from Journal
  without the Blog Editor rules, byte-stable token comparison,
  SanitizeReport, Sanitize, Check, Removals
- cabana: type richeditor (common keys plus size); every create and update
  value sanitized before Fill, non-string values are a 422, removals become
  meta.notices; settings and relation forms refuse the type
- backend lang richeditor.removed_* and markup_changed (en, pl plurals)
- TestSeaglassSmoke, TestCompanionsRichEditorSmoke, README and docs

modules/phrasebook/backend/lang/en/lang.yaml

@@ -323,3 +323,14 @@ myaccount:
   avatar_hint: JPG, PNG, GIF or WebP, up to 2 MB.
   avatar_saved: Avatar saved
   avatar_removed: Avatar removed
+richeditor:
+  removed_elements:
+    one: ":count element was removed: :names"
+    other: ":count elements were removed: :names"
+  removed_attributes:
+    one: ":count attribute was removed: :names"
+    other: ":count attributes were removed: :names"
+  removed_comments:
+    one: ":count HTML comment was removed"
+    other: ":count HTML comments were removed"
+  markup_changed: The HTML filter changed some markup.

modules/phrasebook/backend/lang/pl/lang.yaml

@@ -345,3 +345,20 @@ myaccount:
   avatar_hint: JPG, PNG, GIF lub WebP, maksymalnie 2 MB.
   avatar_saved: Zapisano awatar
   avatar_removed: Usunięto awatar
+richeditor:
+  removed_elements:
+    one: "Usunięto :count element: :names"
+    few: "Usunięto :count elementy: :names"
+    many: "Usunięto :count elementów: :names"
+    other: "Usunięto :count elementu: :names"
+  removed_attributes:
+    one: "Usunięto :count atrybut: :names"
+    few: "Usunięto :count atrybuty: :names"
+    many: "Usunięto :count atrybutów: :names"
+    other: "Usunięto :count atrybutu: :names"
+  removed_comments:
+    one: "Usunięto :count komentarz HTML"
+    few: "Usunięto :count komentarze HTML"
+    many: "Usunięto :count komentarzy HTML"
+    other: "Usunięto :count komentarza HTML"
+  markup_changed: Filtr HTML zmienił część znaczników.