changing signature of IPowerSupply according to issue#2 and propagate changes to RigolDP832 class

I started working on addressing issue #2 (closed).

• changed signature of IPowerSupply to clarify what each function does. Remove initialise, introduce reset.
• added program (implemented in IPowerSupply) and checkCompatibility function
• implemented program for Rigol class as an example
• switch to using exceptions for error handling in IPowerSupply
• replace example power supply programs with powersupply that supports EquipConf

Elisabetta