Improvements to handing vim and vim plugins

[tailhook]

This pull request consists of following:

• Made vimPlugins discoverable by nix-env (just like Fix vimPlugins #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 Vim huge nogui #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.

[bjornfor]

I'd like to merge this, except for the "Remove wrapVim" commit. I don't use the wrapper, and I agree that wrappers in general can be confusing to users (includes me). But I'd like @wizeman to get a say in this, as he wrote the wrapper. Also worth mentioning, the discussion of the wrapper and some alternatives to it, in issue #959.

[tailhook]

Hm, #959 was helpful indeed. It seems that it was agreed that vimrc should be placed in /etc/vim/vimrc, but it hasn't been done. Also my mistake that I thought that vim would read both PREFIX/share/vim/vimrc and /etc/vimrc. It reads single one. So I've added a config to read /etc/vimrc or /etc/vim/vimrc (the first which exists).

I've also added set nocompatible and syntax on by default as its something that everyone wants in 2014. Also it's enabled in both ubuntu and archlinux (I believe debian, and many other distributions too). And upgraded vim to 7.4.335.

Feel free to apply this pull request without removing wrapVim, but it must be fixed if left in nixpkgs. (Also at least no need to add wrapVim into all-packages, because it's meaningless without customization of vimrc itself)

[wizeman]

Since @tailhook's changes source /etc/vimrc (and /etc/vim/vimrc), I am fine with eliminating the wrapper.
Compared to the wrapper, this seems to be a preferred solution (as mentioned in #959).

I have applied these changes on my local nixpkgs and tested that vim compiles, runs and that my /etc/vimrc gets read.

[bjornfor]

Pushed to master (including wrapVim removal). Thanks!