Python rewrite

Hi, here is the Python-rewrite of the debops-scripts.

Notable changed related to the shell-version:
- sourcing `.debops.cfg` is not supported, `.debops.cfg` now is takes as being an `ini`-file
- `ansible_config_hook` is gone, instead you can put sections `[ansible ...]` into `.debops.cfg` which will go into `ansible.cfg` (if the hooks are needed, we will find another ways for implementing them)
- The `padlock`-script is no longer used to decide if secrets are encrypted. This is now done by testing for the encrypted keyfile and the encrypted encfs-config.
- The `padlock` script still exists and has been simplified a lot. Most functionality has been moved into the `debops` python library.
IIRC, `PREFIX ?=` allows you to se the prefix directory in the command line, so that running
```
PREFIX=/opt make
```
becomes possible. Is that change needed here?