Feature/update delete question answers

[YHTerrance]

New functionality:

Questions:

Update:

• Able to update content and topic.
• Only the owner of the question is permitted.
• Maybe also update timestamp in the future Delete:
• Removes the question and all the answers under it.
• When the accounts are removed the rent is returned to the owner of the account (However every removal of an answer or question requires one approval. That is to say, if one question with 7 answers is removed, a total of 8 transactions have to be signed. Maybe we can try to sign multiple transactions in the future?)

Answers:

Update:

• Able to update content of answer.
• Only the owner of the answer is allowed to do so.

Delete:

• Able to delete answer
• Only the owner of the answer or its target question is allowed to delete answers