Update github hook management

[julienvey]

Now handles

• branches push force
• tags

Closes #232

[jawher]

Correct me if I'm mistaken, but with this PR, in the following scenario:

• A user pushes branch B at commit C1
• Suppose it takes sometime for Github to call the build hook
• The user pushes branch B again at commit C2 (on top of C1)

The first hook will start a job with scm ref of B and not the precise commit C1, and so the triggered build will end-up building C2.

[julienvey]

Right, I updated the PR

[jawher]

LGTM