Plot OC-pO2 graph for SCR dives

This commit allows plotting the OC-equivalent pO2 graph for PSCR
dives. This happens in both the cases where there is no external
O2-monitoring AND when there is external pO2 monitoring. The
calculations are only done for PSCR dives and is achieved as
follows:

1) Within plot-info create a pressure-t called OC_pO2 in
   profile.h and populate this variable with the open-circuit
   pO2 values in profile.c.
2) Create a new partialPressureGasItem ocpo2GasItem in
   profilewidget2.h and, in profilewidget2.cpp, initialise it
   to read the plot-info OC_pO2 values and enable its
   display by using the setVisible method. The
   diveplotdatamodel was also touched in order to achieve
   this.
3) Create a pref button that controls the display of OC-pO2 for SCR dives
4) Change the colour of the OC-pO2 grpah to orange
5) Change the connection of the crr_OC_pO2 signal to be appropriate
6) rename the OC_pO2 attribute to scr_OC-pO2

Signed-off-by: Willem Ferguson <willemferguson@zoology.up.ac.za>

qt-models/diveplotdatamodel.h

@@ -64,6 +64,7 @@ public:
 		CCRSENSOR1,
 		CCRSENSOR2,
 		CCRSENSOR3,
+		SCR_OC_PO2,
 		HEARTBEAT,
 		AMBPRESSURE,
 		GFLINE,