This takes the headerbar and navbar and puts them into their own

templates. It makes it a lot easier to read the base template,

particularly with regards to the ordering of blocks and template hooks,

and it also makes it easier to modify these bars without major merge

issues.
It also fixes an issue with overriding the "navbar" block, which

would have resulted in an extra </div>, due to an ordering issue that

wasn't apparent before this change.

Checked that the header and navbars looked and worked correctly on a

variety of pages, including the admin UI.
Enabled the MOTD extension and saw that the bar appeared in the correct

place, showing that the template order was correct.