Create tabset as openblock

[mojavelinux]

Currently, the tabset is created entirely using passthrough blocks. The tabset should instead be created as an open block. This allows it to be better recognized by the referencing system and by code that operates on the parsed document such as a tree processor.

The only drawback of this change is that it will move the location of the div with the "content" class. That will require the following style change for anyone who has been using a custom stylesheet:

old:

.tabset > .content { ... }

new:

.tabset .tab-pane { ... }

It also means that the tab panes will no longer be enclosed, though another div could be added around them if need be.

UPDATE: The new structure is .tabs .tabpanel.