WIP 147 Archive Button

Per: https://assemblymade.com/helpful/wips/147

This PR makes the Archive button actually archive the conversation. There are currently no tests for the javascript portion of the code as I don't think we have settled on our JS testing framework. The JS is also currently inline, might want to extract that out to coffee script in conversations.js.coffee down the line.

In order to make the code simple I created an archive= method on conversation so that we can use the update endpoint in the controller to change the archive status (set archive equal to true to archive it, and false to un_archive it). There may be a better way to do this....