lib/colors: use libtinfo to check terminal capability

lib/colors: use libtinfo to check terminal capability

The current implementation assumes that all terminals supports colors
and users are forcet to use terminal-colors.d/ to disable colors for
some terminals.

This patch checks for maximal supported colors for the current
terminal and colors are automatically disabled for terminals like
vt100.

The patch moves lib/colors.c from libcommon.la to libtcolors.la to
avoid collisions with another utils.

Signed-off-by: Karel Zak <kzak@redhat.com>