Adapt website deployment pipeline to create multi-branch sites

[NeuroShepherd]

That is, every branch receives its own extension or address so that people can always see the development branches live online (but not have them listed as the main website)

[NeuroShepherd]

Notes:

• Every branch needs to be checked out on each deployment
• Only the branch that was edited needs to be re-rendered?
• The content for each branch should be served at lmu-osc.github.io/website-address/BRANCH/