Clone github repository to local automaticly now.

Config your local git repositories path in the plugin configuration(/settings/plugin/redmine_github_hook), pls ensure this path can be writable via redmine. And adding a Git repository to a project (note, this should work whether you want to use Redmine Github Hook or not). Just directly type "git://github.com/xxx.git", that’s all.

+ clone github repository to local automaticly
+ the plugin configuration page to set the local git repositores path.
+ show the scm url in the repository page via ZhuangBiaoWei
+ show the github url in the repository page