Ianjorgensen/message image tag

This is the icon on notes project i worked on the hackathon, i want to code to be there so when we have icons we can use we can simply add the regex's and it will all just work. cc @jebeck  @nicolashery 
I'd prefer to be able to test this branch locally (within tideline) before merging. Can you add what's necessary in the React code for the tideline example to pass this option through so we can uncomment and test?

Also, what's the pigeon icon for and did Sara make it? We have rights to it?