Sort charm config options to match yaml order

[Jeff Pihach]

In writing the Ghost blog charm I have a few configuration options which are required for proper operation of the charm. In the config yaml these options are at the top of the file. However, Juju and the GUI both sort these alphabetically when displaying to the user after deploy which puts the required options mixed among the others in the list and makes the descriptions which reference the location of other options invalid. I'd like investigate different ways to maintain the order from the config.yaml