Remove manual tags, use only generated tags

- change html, head, body from manual to generated tags
- restore compatibility with j2html 1.4.0
- fix https://github.com/tipsy/j2html/issues/185

code_gen/src/main/java/j2html_codegen/generators/TagCreatorCodeGenerator.java

@@ -96,7 +96,7 @@ public final class TagCreatorCodeGenerator {
             "bdi",
             "bdo",
             "blockquote",
-            //"body" BodyTag is managed manually,
+            "body",
             "button",
             "canvas",
             "caption",
@@ -124,9 +124,9 @@ public final class TagCreatorCodeGenerator {
             "h4",
             "h5",
             "h6",
-            //"head", HeadTag is managed manually
+            "head",
             "header",
-            //"html" HtmlTag is managed manually
+            "html",
             "i",
             "iframe",
             "ins",