erp5_core: display erp5 based web sites html

Most ERP5 web sites use a global form wrapping the content.
Modify the html viewer to not drop this content.
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:58:18

passed ERP5.PerformanceTest-Master

00:23:07

failed ERP5.UnitTest-Master

01:36:58

failed ERP5.UnitTest-Master.Medusa

01:54:11

passed SlapOS.Eggs.UnitTest-Master.Python2

00:08:24

passed SlapOS.Eggs.UnitTest-Master.Python3

00:23:47