UI Improvements (Includes changes in the models)

[caroguza]

For a Session:

• Record a feeding as part of a Session

• Force the user to record food for every session, i.e. 0 must be entered if they fed nothing

• when loading previous days data, show it as a placeholder with a button to load it, instead of fully pre-populating it right away

• add DataSetType multiselect to Session (in the same way it's on SessionTask)

For Food:

• Add FoodType with name, unit, then setup both Subject food and Session reward to choose from FoodType

For Tasks:

• Rename Task to TaskType everywhere in the UI, and SessionTask to Task

• Make task sequence number default to 1, 2, 3, ...