Add a Helm-Projectile key to the Helm map

Also explicitly require the `helm-projectile' package.
Show VC projects in ibuffer
Stop using a global TAGS file
Change package install and load machinery

`init-packaged-command' is split into `[with-]require-package'.
Diminish lighters for minor modes

This is basically what diminish.el does.
Use `face-spec-set' rather than `defface'

The face is guaranteed to be defined, so `defface' wouldn't work anyway.