Adding basic calibration script to spsaitActor

According to cloomis, it's worth getting a calibration set each time we cool down and I think spsaitActor is the right place.

the arguments would be:

• nbias : number of bias(default : 15)
• ndarks : number of darks (default:5)
• exptime : dark exptime in s (default 900)

While i'm here, I will also add possibility to take backgrounds