Paperbot: Consider replying on edited messages

[Bueddl]

Right now the bot does not respond with information if a papernumber is added as an edit to a message. This is not very intuitive if you consider someone fixing a papernumber in the message. For example if someone accidently wrote:

[2552]

instead of:

[P2552]

We should consider reacting on changes messages if it does not create too much noise.