Use indirect Signal creation

Otherwise e.g. Constant Conversion is circumvented...
Explicit long type annotation in expensive test
Cleanup Reactivity Interface and prepare split up
Use inferred signals in constant conversion
Complete the split of the syntax into traits
Move syntax traits into files and extract inference optimization
Cleanup imports of syntax files
Cleanup ReactiveOps
Extract SignalOps
Extract VarOps
Extract the propagation
Extract DepHolder and ReactiveEntity traits
Clean whitespace