cmake: generate the shell/perl/python scripts and templates, translations

cmake: generate the shell/perl/python scripts and templates, translations

Implement the placeholder substitution to generate scripted
Porcelain commands, e.g. git-request-pull out of
git-request-pull.sh

Generate shell/perl/python scripts and template using CMake instead of
using sed like the build procedure in the Makefile does.

The text translations are only build if `msgfmt` is found in your path.

NOTE: The scripts and templates are generated during configuration.

Signed-off-by: Sibi Siddharthan <sibisiddharthan.github@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>