EP: Reorganize the org's packages

Aim: This enhancement proposal is to reorganize the packages orgs surrounding reachable set computations.

(this is a draft)

Steps:

1- move set-based algorithms to SetBasedRecurrences.jl

2- split the remaining parts into packages MathematicalPredicates.jl (properties), ReachabilityBase.jl (general infrastructure like ReachSet, ReachSolution, etc.), HybridSystemTransformation.jl (system normalization and simplification) and keep Reachability.jl only for the unification of those packages (and the definition of solve and the discrete-post operators) (also rename the package to ReachabilityAnalysis.jl)

3- do MathematicalSets.jl

4- do MathematicalPredicates.jl

5- better docs for reachability analysis (essential)

6- PR these packages to the general Julia registry

The rest of this wiki is about point 1.