* Models/Instruments/panel-layout1.xml: add a Hobbs meter, not exactly at the same position
as in [1], but close enough. I'd rather not sacrifice the copilot's AoA and OAT gauges.
* Nasal/citation2.nas (JetEngine): add a timer to each engine, measuring how long
/engines/engine[*]/running is true.
(hobbs_timer): new. Feed the Hobbs timer with the maximum of the two values.
(update_systems): call hobbs_timer.update ().
* Nasal/save-state.nas (citation_save_general): save and restore the engine running times.
[1] http://pureflite.com/sites/default/files/forsale/20.jpg
