AIAT-152: Giving up

[pthanvi]

JIRA ticket: https://scottlogic.atlassian.net/jira/software/projects/AIAT/boards/103?selectedIssue=AIAT-152

• Added capability to give up if the user is not sure about an answer for a tree test task
• Added modal for confirmation when the user decides to give up, move to a next task or submit the response
• Added response as 'n/a' if the user decides to give up
• Added new event give_up
• Changed event submit_response to tree_test_completed