Remove lines causing bug
Merge pull request #6514 from czolnowski/entry-pages-bug

Entry pages footer links lead to "Action not found"
Fixing build.
Replace all uses of Piwik_ExitWithMessage (except one) with throwing exceptions & include HtmlMessageException class for exceptions w/ HTML content in their message.
Remove ExitWithMessage function and documented new code.
Adding event so the error page contents can be modified.