Add some optional tools, fix ssl certs

Factorize git objects into a static lib to enhance build
speed, and move lib/git-core to xbin/git-core to set the
right permissions on binaries.

Also, Ignore SSL Cert problem in git config to be able
to clone from github (https://)

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>