Fix #453 Data and talk title displayed incorrectly in the recording UI

The Date column from database's presentation table had "Time".

Closes #481
Close #496 Set travis git clone depth to 1
Fix #427 warn user about erasing new talk info

- Add fieldsEnabled attribute to TalkDetailsWidget

- Add function confirm_add, called on addButton clicked

- Remove fieldsEnabled attribute, add function are_fields_enabled and
unsaved_details_exist, refactor clear_talk_details_widget to
include category, prevent prompt when fields filled by talk selection

- Fix indentation