Improvements to handing vim and vim plugins

This pull request consists of following:
* Made vimPlugins discoverable by nix-env (just like #2984)
* Plugins are moved from `vim-plugins` into `share/vim-plugins` and added to `pathsToLink` (in analogy to `share/emacs`)
* Added apropriate system vimrc, that populates runtimepath with all the plugin directories, according to NIX_PROFILES. This automatically enables plugins from `systemPackages` and from all the profiles installed by nix-env. The latest profile overrides earlier. I.e. you can install different version of plugin in user profile that in system. (This is included only in vim_configurable)
* Removed ``wrapVim`` packages. It doesn't work well. And also it only adds ``vimrc``, what's wrong with ``environment.etc."vimrc".text`` ? (this makes smaller number of vim versions needed, which is a good thing according to #2808) 
* Added few vim plugins: `colorsamplerpack` (nice color schemes), `yankring`, `ctrlp`, `vim-a`, those are super-useful and are packaged at least in archlinux, also they do not update very frequently. So I feel it's ok to add them to repository.