changed keybindings for more familiar ones as requested by defunkt on https://github.com/defunkt/zen/pull/19#issuecomment-43599926
added more specificity to avoid conflicts in the future, as suggested by @izuzak on https://github.com/atom/atom-keymap/issues/33#issue-34734639
no need for 3 different cson files for platform specific keymaps, consolidated into one, tested locally, it works
removed 3 useless files (keymaps/*.cson)
Keep the old cmd-ctrl-z shortcuts too
Merge branch 'familiar-keybindings'