build: Build with colors

Based on tpruvot/chirayudesai's commits, add some color to stdout
and but make it a little easier to customize. Colors are now mapped to
categories and can be edited in Makefile if you or your terminal's
background color do not like them. Defaults:

host stuff: yellow
target stuff: cyan
install/copy: green
filesystem/images: green
imports/exports/includes/notices: green
deletes: red
complete msg: bold green

Coloring can be disabled with "export BUILD_WITH_COLORS=0"

Change-Id: Idcfe9bbf925759f88425f914269855da05c5eef0

Conflicts:
	core/Makefile
	core/main.mk