add method to call set_lock_position server API

[agalasso]

request from David C

My goal is to select several targets for a night and check if the telescope can manage automatically to place them in the slit and acquire spectra. I think it is doable using Adjust Lock Position and Sticky Lock. I have tried it manually and it works, but i do not know how to send numbers, with a script, to the Adjust Lock Position. 

 

The procedure would run roughly this way:

 

-send the telescope to RA, DEC.

-start guiding

-acquire and save an image with PHD2

-plate solve calculating the center (RA, DEC) of the image

-calculate the offset in pixels (Δx, Δy) from the target to the center of the slit

-add that offset to Adjust Lock Position numbers

-wait a few minutes and recheck with a new plate solve

-recenter if necessary (working manually i hardly never need a recenter, it normally works the first time if the offset is calculated correctly!)

-start acquiring spectra

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