change layers to be plural and sources are singular
change layers to be plural and sources are singular

* with the exception of Data layer and DataSource
* also add messages to NotImplementedError
* new layer names and their sources
* source: DataSource, layer: Data
* source: Calc, layer: Calculations
* source: Formula, layer: Formulas
* source: Output, layer: Outputs
* source: Simulation: layer: Simulations

mikofski/Carousel,SunPower/Carousel,mikofski/Circus