Create a mechanism to upgrade the TET's data structures, and do some cleanup.

The TET now has a mechanism to upgrade TE blocks to the latest data structures,
though backwards compatibility is not currently dealt with.
Also clear unneeded cell arrays that held text.  I'm not sure why that existed,
 and at least the quadratic example has both cell and non-cell arrays for
holding the text, speaking to the uselessness of the array.  Thus remove the
array as an upgrade mechanism.  This shrinks down the size of the TE blocks
some too!