instrumentation of microScreen.model.pHMeter

[pixelzoom]

Something I noticed while working on another issue...

Instrumentation of the pH meter mode in Macro screen looks like this:

-phScale
  -microScreen
    -model
      -pHMeter
        valueProperty
        -probe
          positionProperty

There are a few problems here:

• valueProperty is never updated, always null
• this meter doesn't have a separate movable probe, so both probe and positionProperty are irrelevant
• it's created in the model, but not actually used in the view

Like the My Solutions screen, there's no need for microScreen.model.pHMeter -- it has no moving parts, and its pH is always the same as the solutions. So it should be removed.

[pixelzoom]

microScreen.model.pHMeter has been removed. @arouinfar please review in master, let me know if you have any questions about this.

[arouinfar]

That all sounds reasonable to me @pixelzoom, and it looks good in master.