Full renaming (package/module/class)

[nhuet]

The goal is to have more consistency in names choices across the
library, between and even within problem type.

• We use camel case for classes
• For each problem,
  • the solvers are stored in a subpackage "solvers" (was sometimes "solver"),
    in a module with a short name "{technology}" without adding
    "solver" or the problem name
  • the base solver class is also in solvers, accessible directly via
    discrete_optimization.{problem}.solvers,
  • the solvers_map is accessible in discrete_optimization.{problem}.solvers_map,
  • the solver class name follow the logic {Technology}{Problem}Solver,
  • the problem class name is {Problem}Problem,
  • the solution class name is {Problem}Solution,
• To be consistent, problem names which are acronym keeps only their
  first letter in uppercase: Rcpsp, Fjsp, Jsp, Gpdp, Vrp, Tsp
• pickup_vrp becomes Gpdp (was already used for problem, solution and
  some solvers)
• all CP (resp. LP) becomes generally Cp (resp. Lp), to avoid confusion
  between (formerly) CPM_RCPSP and CP_MRCPSP.
• MRCPSP -> MultimodeRcpsp
• RCPSP_MS -> MultiskillRcpsp

For instance the cp-sat solver for coloring can be imported via

from discrete_optimization.coloring.solvers.cpsat import CpSatColoringSolver

and the problem class via

from discrete_optimization.coloring.problem import ColoringProblem

• tests and examples names are also harmonized (less prefix/suffix)

[g-poveda]

thanks for the big work