First stable r2ogs for installation

• Run devtools::check() without warnings -> #86 (closed)
• Be able to install via devtools::git_install() or via git clone <repo> and devtools::install(<local_repo>)
  • here, the issue with reticulate has to be solved by including install.packages("reticulate") reticulate::install_miniconda() reticulate::py_install("vtk") in the installation routine --> handled in #64 (closed)