Improve powersupply tool

• Add set-current command to set current sourcing (see #15 (closed))
• Both set-current and set-voltage now take a second optional argument that sets the protect for the other field
• Use ~/.labRemote/hardware.json as a default config file if it exists. Can be overridden by the --equip option
• Remove Rigol default as it is not very fair to other power supplies