Add support for configuration generation

[esyr-rh]

Current module.config generation code relies on config template, which significantly limits the ability to generate proper configuration in complicated cases (think prepare_sources with bunch of -C options). It would be much better if module.config can be generated from scratch based on the actual configuration. This would also significantly improve quality (and usefulness) of dump_config command. In order to accomplish that, several things have to be done:

• Add ability to store comments to the internal configuration representation.
• Add ability to store configuration option origin to the internal configuration representation.
• Add serializer method to DDiskitConfig class that allow specifying configuration options from which origins should be serialized.