Frontend/social login

This PR support Twitter login.

Known Issue. (But I don't know solution.)
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1. in `make html`, cause 2 warnings about JSON-LD. But it is not related this PR.
2. It is not styled with bootstrap. It will be fix after merge #47.
3. Tests was missing. I am in coding now.
Yes. I'll remove it. Template path in other file such as `ontology.py` will fix another branch.