Support different prefixes

Instead of change branches just beginning with "change/*" that should be able to have any prefix: "feature/*", "bug/*", "hotfix/*" etc.

The start command would work something like this:

```
change start example -p feature
```

The long-term intention is to have "bug" and "feature" commands that in-tern use "change":

```
feature start example
```

**Note**: The `-p` argument is optional, if the user leaves it off they'll get a `change/*` branch.

- [x] accept
- [x] checkout
- [x] delete
- [x] list
- [x] publish
- [x] stage
- [x] start
- [x] update