Can we make the Ark simpler?

Headers now have much more limited uses than they had in version 1 of the Ark. They are used to describe email content, to indicate that an LSec contains LEnts, and in DescriptorUnits (where, I expect, they may be used heavily).

One thought then is to indicate in a Topic's DescriptorUnit the applicability of Headers. We can also replace the existing ch command with two commands, one for editing headers and the other for editing TextContent. Now most user will not need to know what a Header is.