Show viewlet only when collective.jekyll is installed

Add more documentation
Forgot the README renaming in setup.py
Add controlpanel to activate / deactivate symptoms

Save settings in configuration registry
Do not display Jekyll viewlet if no activated symptom for context
Add plone.app.registry dependency
Delete .mo files
Change icon to stethoscope
Remove obsolete documentation
Merge pull request #3 from laulaz/control-panel

Add controlpanel to activate / deactivate symptoms