Change name of leftAddendLabelPlacementProperty

[marlitas]

From the phet-io design doc:
"No idea what this does → change name of PhET-iO ID because I think this is only relevant for the number line toggle under the counting area"

It is indeed referencing the toggle beneath the number line.

What would we like to call it?

[catherinecarter]

Let's call it numberLineCountFromPosition

This will afford a connection to the accessible name (#78) where the toggle has the name of "Count on, switch to count from zero" or "Count from zero, switch to count on"

I'm not sure how the structure of the tree will look, and I don't know if the first two words need to be numberLine, but a note that this toggle only applies to the number line representations on the Ten, Twenty, and Sum screens.