Frontend/social login

This PR support Twitter login.

Known Issue.
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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. All tests about web was skipped. Because social login test need secure environment variable. but it is not supported in PR.
4. Alembic patch was missing. I'll add it after review.