New commits for the html5as tutorial
All the commits taking in count new changes such as the new recipe switch-softwaretype or Eric's merge request: !1010 (merged).
I also added a new and final commit "html5as: switch to slapos.recipe.build" (see my MR !1012 (merged)) after the current final one "html5as: add sla computer parameter" (current tutorial). However, I'm not sure what name should be used.
The aim of this new commit is to create an "advanced" stage in the tutorial.