Frontend/social login

This PR support Twitter login.

Known Issue. (But I don't know solution.)
-----------------
1. in `make html`, cause 2 warnings.
```console
(cliche)item4-macbook-proui-MacBook-Pro:docs item4$ make html
sphinx-build -b html -d _build/doctrees   . _build/html
Running Sphinx v1.2.3
loading pickled environment... done
WARNING: intersphinx identifier 'flask_OAuthlib' is not alphanumeric
building [html]: targets for 9 source files that are out of date
updating environment: [config changed] 31 added, 0 changed, 0 removed
/Users/item4/.virtualenvs/cliche/lib/python3.4/site-packages/SPARQLWrapper/Wrapper.py:100: RuntimeWarning: JSON-LD disabled because no suitable support has been found
  warnings.warn("JSON-LD disabled because no suitable support has been found", RuntimeWarning)
reading sources... [100%] test                                                                                     
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] test                                                                                      
writing additional files... genindex py-modindex search
copying static files... WARNING: html_static_path entry '/Users/item4/Projects/cliche/docs/_static' does not exist
done
copying extra files... done
dumping search index... done
dumping object inventory... done
build succeeded, 2 warnings.

Build finished. The HTML pages are in _build/html.
```

2. It is not styled with concise.css. It will be fix after merge #41