Fix typo
Fix void list error

if the list is void, you can't access its first element :)
Avoid duplicate menu population
Insert default timeslots on workshop add
Generate the worshop's datetime

We take the date of the first timeslot (in both edition and add)
Allow global attendance sheet export
Move duration to integer (for stats)
Grid widget : push the hidden widgets at the bottom

This way we can handle a clean layout (if the id is hidden in first, we
get an undesired left-margin)
Exclude relationships from the customer form
Clean the customer views and enhance model
Avoid the creation of a void row
Don't pass the id for edition (use the context instead)

If not, a malicious user may edit any customer
Staticmethods are not handled by the BaseListView
Remove the customer schema (now handled by colanderalchemy)
End cleaning customer forms
Fix workshops tests
Fix fake database script to fit customer model
Add a new models/widgets module for colanderalchemy widgets
Usefull Dummy class (don't have mock's problems with name attr)
Little fixes on customers