Subassembly - Parameter Expression Editor

[fcernst]

Add a very simple basic Expression Editor, much like we have now for Labels, that we can apply within the common subassembly parameters (i.e, such as slope, width and depth).

Add the following basic three API functions to the Expression Editor:

1. Baseline.Station()
2. Baseline.Offset()
3. IF(expression=, true, false)

Then we can do things like... If we are beyond Sta. 2+00 make the asphalt depth 9", otherwise make it 6":

IF(Baseline.Station(XX)>200,0.75,0.5)

**This would also allow us to easily linearly transition any of these subassembly parameter values as a function of Station position on the Baseline or Offset.

For example, this would also address the Daylight Slope Transition request.

[fcernst]

We would aslo want Baseline.Start, Baseline.End and Baseline.Grade.

...Essentially the functions that are in the Baseline Class from Subassembly Composer.