Add case of no tirgger from github, Use SCM

Our Jenkins is local Ethernet and is not open to triggers from github.
We add the option to use the plug in taking the credential from the SCM section in jenkins.
for example:
https://user:password@github.com/kenshoo/github-plugin.git
1. Check if no triggers.
2. Get the credential from the SCM.
3. Login to github
4. Get the github repository.
5. Set the build status to the branch/pull request