zsh-migration: remove submods

Will be using oh-my-zsh plugins instead.
Removed SSH config files

Will be machine-specific for me.
Moved source files to "disable" them

Not as useful for me, but might reuse/adapt them later.
"disable" somes files from /link

Same ideas as .source, might reuse them later.
copy adapted ".osx" from Mathias' dotfiles

More sensible OSX defaults
Added Brewfile and zsh
Removing ruby/gems from init script

Will be installing those via Homebrew.
Added script to set default shell to zsh
Updated dotfiles to clone my fork