Timed/delayed settable

Description

Add a settable that waits until a certain amount of time has expired before setting the value.

A function that wraps around a settalbe to create a new settable with identical properties but that waits until a certain time has expired before setting the next value.

Implementation could be different. Also relates to #128 (closed) and working through the use-cases properly.

class DelayedSettable():
    def __init__(self, settable, delay=0):
        self.settable = settable
        self.previous_value =0
        self.delay = delay


    def set(self, value):
        while time.time()-self.previous_time< self.delay:
            # wait
            time.sleep(0.01) # wait a bit, could also be a pass 
        self.previous_time = time.time() # update time before setting next datapoint 
        self.settable.set(value) 

Motivation

Based on feedback from @peendebak: In many 1D and 2D scans for spins we want to add a delay for setting a parameter. This could be achieved through a special settable as above.