Improved wikitext escaping of headings

* Headings dont need to escaped unless they are in the extremities
  In some cases (Ex: "==bogus== 
a
"), the escaping didn't
  account for additional non-heading chars in eol position.

* The fixes now lead to 2 more wt2wt, 2 more html2wt and 32 more
  passing selser tests.

* Updated parserTests-blacklist

Change-Id: I65cfa51c7508145881c6b370d9ed452cc678903b