zypper.8: fix typo
PropertyTable: remove unneeded base class
New colorization code

* Avoid using "grey" and "white" in the default color preset,
  as that plays bad with white backgrounds.
* Use bold for prompts, and colorize the section headers.
* Remove double spaces between letter groups.
* Only colorize each letter group, rather than the first letter
  of every package.
* Do not consider downgrades to be negative, but rather a change.
new ansi.h: core for colored output ColorString ColorStream
Config: switch to ansi::Color and cleanup
define ColorContext based on ansi::Color; remove legacy color code
Cleanup using ansi::Color
Add --[no-]color global option
Merge branch 'colorization'

Conflicts:
	src/Config.cc
	src/Config.h
	src/Summary.cc
	src/Table.cc
	src/utils/colors.cc
	src/utils/colors.h
	src/utils/prompt.cc
	zypper.conf
changes 1.12.0