monaco_editor: make editor really full page

using the solution from https://stackoverflow.com/a/45753938

and also a rule to disable body margin from user agent stylesheet, in
chrome there's a 8px margin.
1 job for arnau-RD-Components-providesIFoo in 0 seconds
Status Job ID Name Coverage
  External
failed ERP5.UnitTest-TestRunner1

01:50:15