Restructuring some of the initialization code.

Restructuring some of the initialization code.

The general idea is to help clean up some aspects of the FDM init and be
able to provide startup conditions in a less ambiguous manner.

Previously, things like positions, orientations, and velocites were set on
"the bus".  These had to be read by the FDMs which then were supposed to
initialized themselves to those values and turn write around and start
modifying those values.  It was messy and cumbersome.

Now, all the initial fdm conditions are written to a sub-[property-]tree
under /sim/presets/

The values in /sim/presets/ always stay set to what the user has specified.
The user can change these at his/her liesure, and then request a "reset"
which will reset to the new conditions.  I don't even want to say how this
worked before. :-)

Now, an script, or gui interface can stage a set of initial conditions while
the sim is running (without disrupting it), and then call "reset" to commit
the change.

People who should worry about all this are FDM writters, and a small few
others who care about over all program structure and flow.