fixes #6806
Merge remote-tracking branch 'origin/master-3.1' into issue-6806-allow-index.html-as-homepage
#6806 added validation in ContentletAPI for htmlpages
#6806 added validation message in ContentletAPI for htmlpages
#6806 allow pages without extenstions to be renamed in the browser
#6806 allow rename in browser even extension
Merge pull request #6807 from dotCMS/issue-6806-allow-index.html-as-homepage

fixes #6806