New field in Mom's Stories competition

The Mom's Stories competiion on the MAMA site uses the ```jmbo-your-words``` app to enable submitting of stories by the young mothers visiting the sites. They have a requirement to display terms and conditions per competition. The solution was implemented as a new ```MomsStoriesCompetition``` model class in the ```mama``` app inside the MAMA website project. The model was given the ```app_label='jmboyouwords'``` meta attribute, hence the migration ended up in the ```jmbo-your-words``` app. The model add a new ```terms_and_conditions``` field to enable capturing the terms and conditions for the competition. This was implemented as part of the solution to MAMA-170.