Clean up installation instructions.

Remove git as its installed through homebrew now. Update installation
command to clone repo then run laptop script locally.
Add coda file that git clones CoffeeScript and Bash modes.
Simplify all npm packages installed into one command.
Simplify all ruby gems installed into one command.
Clone projects dynamically so its easy to add or remove by project.
Update to install bash-completion and source scripts and new coda one.

No need to install credential helper as installing from Homebrew will
include it by default. The config in dotfiles sets helper to
osxkeychain.