Temporary fixes for some trigger and saving issues

[ywkure]

Dirty fixes made for the following issues:

1. It stops because it didn't receive data from stytra during the waiting time (1 s) at the beginning of a plane. The time it takes ranges from 6 ms to at least 2.5 s. Solved by waiting 5 seconds.
2. It creates the splitdataset without the last plane because it finishes before receiving the last frame of the last plane. Solved by waiting 5 seconds for the last frame.
3. It moves double the z step size when moving to the next plane because it triggers the motor twice. Solved by forcing the internal frame count to have a small number once the z motor is moved.
   (4. Sometimes the z motor moves unintentionally during imaging. Not sure if it's a software problem, but now the motor is turned off after starting a plane.)

[nvbln]

I will merge this. Since the fixes are meant to be temporary, I opened issues #30 and #31 to track this.