Bug 124539

xml/core module needs to be cleaned up for the following reasons:

- A lot of unnecessary classes related to "scenario" exists.
- The module bundles both model and UI related classes together. In principle, this is not good. Potentially there can
be a cyclic dependency. The UI related classes may want to depend on some other module X, which already depends on xml/core.
- A lot of code from xml/core (related to Loaders, DOs, encoding) can be reused elsewhere if xml/core is divided into a
separate module.

Here is my proposal:
1. cleanup all junk in xml/core.
2. xml/core is already a public module, so lets keep all the API and impls here. Nothing changes for the consumers.
3. Move rest of the stuff Loaders, DOs, UIs etc. to a new module xml.
4. This new module will have a lot of common code that can be reused by various modules. They will be friends.