Expose full API of lightsources in design model, not in internal model

[ichinii]

current status

DesignSource exposes common API among different lightsources. Compiling a DesignSource into one of the lightsources releaves new API specific for that lightsource.

motivation

• API in different places is confusing
• clear differentiation between design model and internal model
• internal model should be minimal and compact
• conceptually internal model would not be mutated by users at all. thus, internal model data can be constant
• internal model should be designed to meet favors of accelerators

request

remove everything that should be design API from the internal model to the design model