Support for 2-channel scopes?

[mattncsu]

Hello, I am testing keyoscacquire with a Keysight DSOX1202G and when issuing the scope = koa.Oscilloscope('LONG ADDRESS') command, the library responds with:
Connected to: KEYSIGHT TECHNOLOGIES DSOX1202G (serial CN######)

Then after a delay there is a timeout when trying to query ':CHAN3:DISP?'. Since this is a two channel scope, polling channel 3 causes an error. Changing the range(1 to 5) to range(1 to 3) on lines 319 and 326 of oscilliscope.py clears the error but now it is hardcoded for 2 channels.

Since there isn't a standard SCPI command to determine the number of channels on a scope, perhaps channels could be added as a parameter when initializing.