Add "collected" field to add/edit Animal form

[metamoni]

As part of #796 we're adding a collected field to the Animals table. When this is true, we need to provide a non-null entry_point, or else we'll get a validation error. When it is false, the animal was spawned and an entry_point field is not needed (this will be automatically populated with an empty string in the database).

Once this PR is merged, add a "Collected" field with two radio options - "Yes" and "No". If the user selects "Yes", we should display a required "Entry Point" field where the user will enter the location.

Add changes in app/views/animals/_form.html.erb. The new "Collected" and "Entry Point" fields could be added under the "Entry Date" field.