Add date fields to the ingredient model

* creation_date is set on adding the ingredients
* update_date is set on updates

This fixes Issue #15
Move some code to new 'utils' application

--HG--
rename : wger/workout_manager/urls.py => wger/urls.py
rename : wger/workout_manager/constants.py => wger/utils/constants.py
rename : wger/manager/context_processor.py => wger/utils/context_processor.py
rename : wger/workout_manager/generic_views.py => wger/utils/generic_views.py
rename : wger/workout_manager/helpers.py => wger/utils/helpers.py
rename : wger/manager/utils.py => wger/utils/language.py
rename : wger/manager/utils.py => wger/utils/pdf.py
rename : wger/workout_manager/widgets.py => wger/utils/widgets.py
rename : wger/workout_manager/wsgi.py => wger/wsgi.py
Serve special files with correct content type

--HG--
rename : wger/manager/static/manifest.webapp => wger/manager/templates/manifest.webapp
Set the is_staff attribute for the default admin user

This is needed to access django's admin application.
Rename function
Add start script
Mark help text to be translated
Improve usability when creating new sets

The settings for each exercise set can now be also edited directly from the
same window. Additionaly, a slider is used to edit the number of sets.
Merge