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.

- [ ] accept
- [ ] checkout
- [ ] delete
- [x] list
- [ ] publish
- [ ] stage
- [x] start
- [ ] update