Make R work with R classes and changes from volesti develop

[vfisikop]

This is a major PR that consist of mainly the following changes:

• combine functionality from develop of volesti (new functions) with structure (R classes instead of modules) from current CRAN package.
• remove submodules and add needed code as part of the package (I found it more convenient especially in the case of CRAN where there are a lot of limitations in the package structure) NOTE: some commits in this PR experiment with submodules and git sparse-checkout and I kept them for future reference (see e.g. github actions)
• lpsolve structure is changed, now it uses the same structure as lpSolve cran package, which is easier to maintain and update. Update can be performed by following the following steps:
  • download new lpsolve source code inside src
  • copy and update Makefile in lpSolve/src
  • check and update (if needed) the lpSolve_patches
  • update the copyright notes (version number)