start on being able to comment out cells by marking them Text

crashy so far
Merge branch 'develop' into comment-cells

Conflicts:
	htdocs/js/rcloud_bundle.min.js
accept that github thinks Text === null

support Text mode better too

ingrain it deep in buffer_model where it won't be repeated
distinguish between undefined and null
remove all the other places we were working around this

initialize cell language map in environment

a few things still broken in this commit
Merge branch 'comment-cells' into develop
disable text cells

but keep the ability in there