Add a button to delete an entire thread of comments

Steps to reproduce:

• add a comment on a page such as http://localhost:8080/xwiki/bin/view/Sandbox/TestPage1
• add several replies for the comment (see image AddComments-step1)
• delete the first comment (not the replies)

Result:

• the user does not have a possibility to delete the entire thread
• it's good you have the option to delete individual replies, but to delete the entire thread you would need to click on each individual "Delete" button