Switch to official Flask-Login 0.3.0

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Point to a commit of official Flask-Login.
New Flask-Login is not on PyPi yet so point to GitHub.
Merge pull request #909 from PyBossa/issue-switch-official-flask-login

Switch to official Flask-Login 0.3.0
Test Slack.
Use latest version.
New strings.
New strings translated.
Fixes for the translations
Translation fixes.
Use latest version
Improvements to translations.
Update translations.
Fix a typo
Fixes to translations
Fixes for translations
Fix translations.
Improve i18n.
French updates.
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Merge pull request #910 from PyBossa/issue-fix-warm-cache

Compute stats always for featured projects.
Merge branch 'master' of github.com:PyBossa/pybossa into issue-translations