Order of Run Start Broadcasts

Currently the following happens and PL sends the following BC sequence
when a run is started:

START RUN ENGINE:

• The model is initialised for run (phase 1)
  BC _Preinit Start
  BC _Model loaded (if its an initial run)
  BC _PreInit End
• The model is initialised for run (phase 2)
  GC _Run Start
• model pauses or continues depending on options

The 2 stage init process was from an era when certain objects could not
be changed once the run was going but the modeller needed an ability to
initially set them up. (the conveyor is still like this). Also item "preloading" happens in the
second phase of the initialisation of the run.

Two changes I'd like to make:

• move the _Model Loaded BC to occur just before _Run Start. This will allow it to trigger messages, etc. which it cant at the current time it
  is sent
• reduce use and eventually eliminate dependence on the 2 _PreInit
  broadcasts by modellers.

(followup: these BCs wont be removed as they are useful for modeller's setup use)

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idkbase note 205