antiflood option for comments

[micheelengronne]

Attempt to solve #189

Add an option --comment-antiflood to avoid a flood with the same comment.

[micheelengronne]

This patch checks that the last comment body is not the same as the one that would be written.

It works.

The only anti-pattern that I can see is when an event is triggered that does not add any note to the MR (like retriggering manually the pipeline).

[micheelengronne]

Hum, I have to pass more time figuring how the mock works to add the new endpoint. Any hint ?