add new plugins (mostly language-specific), make some fixes

Add:
- Lokaltog/vim-easymotion
- jimenezrick/vimerl
- klen/python-mode
- othree/html5.vim
- moll/vim-node
- marijnh/tern_for_vim
- othree/javascript-libraries-syntax.vim
- leshill/vim-json
- sheerun/rspec.vim
- tpope/vim-cucumber
- tpope/vim-haml
- kana/vim-textobj-user
- kana/vim-textobj-indent
- tyru/open-browser.vim

Change jelera/vim-javascript-syntax to zenbro/vim-javascript-syntax.

Improve ag behaviour.