Restructure el-get configuration

1) Custom recipes are moved from init.el to el-get-recipes/
2) Custom recipes that just had an :after block are deleted and contents
moved to init.el
3) Add machine-specific el-get-to-install, for such machines that don't
need all packages (like AUXTeX, scala-mode, ensime, etc.) This file is
in .gitignore
Add .jpg and .jpeg to org-file-apps