Add --with-exceptions option

We need a way of removing certain documents after we clone the database, otherwise the validation functions are copied from tools to tools-dev and therefore developers cannot work on tools-dev. This PR allows that, and fixes a bug that made the option --so-security to be ignored. Other additions:

* Config() singleton class that holds configuration
* ```--set-roles``` option that reads from .couchrc the roles to set after cloning:

```
[roles]
members = list,of,members
admins = list,of,admins
```