Scan improvements

• in scan, only print updated motor(s) position(s) if the output is a tty
• allow to create a scan object without executing the function. Ex: my_scan = ascan(sax, 0, 10, 100, 0.1, run=False, return_scan=True)
• support temperature channels as counters in scans
• include motion time estimation in statistics
• fix mixed counter values and header bug in output. I had to introduce a change in the scan_data event value from [<value>, ...] to {<channel name>: <value>}. I assume nobody else is listening to this event yet.
• fix scan event callback of bliss web shell